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Mobile telephony
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Most current mobile phones connect to a cellular network of base stations (cell sites), which is in turn interconnected to the public switched telephone network (PSTN) (the exception is satellite phones).
rding to internal memos, American Telephone & Telegraph discussed developing a wireless phone in 1915, but were afraid deployment of the technology could undermine its monopoly on wired service in the U.S.
In 1947 Bell Labs was the first to propose a cellular network.
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Encyclopedia
Most current mobile phones connect to a cellular network of base stations (cell sites), which is in turn interconnected to the public switched telephone network (PSTN) (the exception is satellite phones).
History
According to internal memos, American Telephone & Telegraph discussed developing a wireless phone in 1915, but were afraid deployment of the technology could undermine its monopoly on wired service in the U.S.
In 1947 Bell Labs was the first to propose a cellular network. The primary innovation was the development of a network of small overlapping cell sites supported by a call switching infrastructure that tracks users as they moved through a network and pass their call from one site to another without dropping the connection. Bell Labs installed the first commercial cellular network in Chicago in the 1970s.
Japan's first commercial mobile phone service was launched by NTT in 1978. By November 2007, the total number of mobile phone subscriptions in the world had reached 3.3 billion, or half of the human population (although some users have multiple subscriptions, or inactive subscriptions), which also makes the mobile phone the most widely spread technology and the most common electronic device in the world.
The first mobile phone to enable internet connectivity and wireless email, the Nokia Communicator, was released in 1996, creating a new category of multi-use devices called smartphones. In 1999 the first mobile internet service was launched by NTT DoCoMo in Japan under the i-Mode service. By 2007 over 798 million people around the world accessed the internet or equivalent mobile internet services such as WAP and i-Mode at least occasionally using a mobile phone rather than a personal computer.
Cellular systems
Mobile phones send and receive radio signals with any number of cell site base stations fitted with microwave antennas. These sites are usually mounted on a tower, pole or building, located throughout populated areas, then connected to a cabled communication network and switching system. The phones have a low-power transceiver that transmits voice and data to the nearest cell sites, normally not more than 8 to 13 km (approximately 5 to 8 miles) away.
When the mobile phone or data device is turned on, it registers with the mobile telephone exchange, or switch, with its unique identifiers, and can then be alerted by the mobile switch when there is an incoming telephone call. The handset constantly listens for the strongest signal being received from the surrounding base stations, and is able to switch seamlessly between sites. As the user moves around the network, the "handoffs" are performed to allow the device to switch sites without interrupting the call.
Cell sites have relatively low-power (often only one or two watts) radio transmitters which broadcast their presence and relay communications between the mobile handsets and the switch. The switch in turn connects the call to another subscriber of the same wireless service provider or to the public telephone network, which includes the networks of other wireless carriers. Many of these sites are camouflaged to blend with existing environments, particularly in scenic areas.
The dialogue between the handset and the cell site is a stream of digital data that includes digitised audio (except for the first generation analog networks). The technology that achieves this depends on the system which the mobile phone operator has adopted. The technologies are grouped by generation. The first-generation systems started in 1979 with Japan, are all analog and include AMPS and NMT. Second-generation systems, started in 1991 in Finland, are all digital and include GSM, CDMA and TDMA.
The nature of cellular technology renders many phones vulnerable to 'cloning': anytime a cell phone moves out of coverage (for example, in a road tunnel), when the signal is re-established, the phone sends out a 're-connect' signal to the nearest cell-tower, identifying itself and signalling that it is again ready to transmit. With the proper equipment, it's possible to intercept the re-connect signal and encode the data it contains into a 'blank' phone -- in all respects, the 'blank' is then an exact duplicate of the real phone and any calls made on the 'clone' will be charged to the original account.
Third-generation (3G) networks, which are still being deployed, began in Japan in 2001. They are all digital, and offer high-speed data access in addition to voice services and include W-CDMA (known also as UMTS), and CDMA2000 EV-DO. China will launch a third generation technology on the TD-SCDMA standard. Operators use a mix of predesignated frequency bands determined by the network requirements and local regulations.
In an effort to limit the potential harm from having a transmitter close to the user's body, the first fixed/mobile cellular phones that had a separate transmitter, vehicle-mounted antenna, and handset (known as car phones and bag phones) were limited to a maximum 3 watts Effective Radiated Power. Modern handheld cellphones which must have the transmission antenna held inches from the user's skull are limited to a maximum transmission power of 0.6 watts ERP. Regardless of the potential biological effects, the reduced transmission range of modern handheld phones limits their usefulness in rural locations as compared to car/bag phones, and handhelds require that cell towers be spaced much closer together to compensate for their lack of transmission power.
Some handhelds include an optional auxiliary antenna port on the back of the phone, which allows it to be connected to a large external antenna and a 3 watt cellular booster. Alternately in fringe-reception areas, a cellular repeater may be used, which uses a long distance high-gain dish antenna or yagi antenna to communicate with a cell tower far outside of normal range, and a repeater to rebroadcast on a small short-range local antenna that allows any cellphone within a few meters to function properly.
Tariff models
When cellular telecoms services were launched, phones and calls were very expensive and early mobile operators (carriers) decided to charge for all air time consumed by the mobile phone user. This resulted in the concept of charging callers for outbound calls and also for receiving calls. As mobile phone call charges diminished and phone adoption rates skyrocketed, more modern operators decided not to charge for incoming calls. Thus some markets have "Receiving Party Pays" models (also known as "Mobile Party Pays"), in which both outbound and received calls are charged, and other markets have "Calling Party Pays" models, by which only making calls produces costs, and receiving calls is free. An exception to this is international roaming tariffs, by which receiving calls are normally also charged.
The European market adopted a "Calling Party Pays" model throughout the GSM environment and soon various other GSM markets also started to emulate this model. As Receiving Party Pays systems have the undesired effect of phone owners keeping their phones turned off to avoid receiving unwanted calls, the total voice usage rates (and profits) in Calling Party Pays countries outperform those in Receiving Party Pays countries. To avoid the problem of users keeping their phone turned off, most Receiving Party Pays countries have either switched to Calling Party Pays, or their carriers offer additional incentives such as a large number of monthly minutes at a sufficiently discounted rate to compensate for the inconvenience.
In most countries today, the person receiving a mobile phone call pays nothing. However, in Hong Kong, Canada, and the United States, one can be charged per minute, for incoming as well as outgoing calls. In the United States and Canada, a few carriers are beginning to offer unlimited received phone calls. For the Chinese mainland, it was reported that both of its two operators will adopt the caller-pays approach as early as January 2007.
The asymmetry of Receiving Party Pays vs Calling Party Pays means a person in a RPP country (such as the US) calling a CPP country (e.g., Europe) pays both the calling charge and the receiving charge and the international toll, while the recipient pays nothing as usual. This is generally reflected in a significantly higher rate to mobile numbers (e.g., 25c/minute vs 3c/minute to a landline). Going the other way there is no difference in rate because the recipient pays the receiving charge. This can make people in CPP countries reluctant to call mobile numbers in RPP countries. There is further asymmetry in that an RPP user can choose a carrier with cheaper incoming minutes, while a CPP user cannot choose a carrier with cheaper RPP-to-CPP rates because these are quoted nationally rather than per carrier. This allows carriers in CPP countries to charge higher rates than would be tolerated in RPP countries.
While some systems of payment are 'pay-as-you-go' where conversation time is purchased and added to a phone unit via an Internet account or in shops or ATMs, other systems are more traditional ones where bills are paid by regular intervals. Pay as you go (also known as "pre-pay") accounts were invented simultaneously in Portugal and Italy and today form more than half of all mobile phone subscriptions. USA, Canada, Costa Rica, Japan and Finland are among the rare countries left where most phones are still contract-based.
One possible alternative is a sim-lock free mobile phone. Sim-lock free mobile phones allow portability between networks so users can use sim cards from various networks and not need to have their phone unlocked.
Impacts
Human health and behaviour
Since the introduction of mobile phones, concerns (both scientific and public) have been raised about the potential health impacts from regular use. But by 2008, American mobile phones transmitted and received more text messages than phone calls. Numerous studies have reported no significant relationship between mobile phone use and health, but the effect of mobile phone usage on health continues to be an area of public concern.
For example, at the request of some of their customers, Verizon created usage controls that meter service and can switch phones off, so that children could get some sleep. There have also been attempts to limit use by persons operating moving trains or automobiles, coaches when writing to potential players on their teams, and movie theater audiences. By one measure, nearly 40% of automobile drivers aged 16 to 30 years old text while driving, and by another, 40% of teenagers said they could text blindfolded.
Mobile phone dermatitis
According to Reuters, The British Association of Dermatologists is warning of a rash occurring on people’s ears or cheeks caused by an allergic reaction from the nickel surface commonly found on mobile devices’ exteriors. There is also a theory it could even occur on the fingers if someone spends a lot of time text messaging on metal menu buttons. Earlier this year Lionel Bercovitch of Brown University in Providence, Rhode Island, and colleagues tested 22 popular handsets from eight different manufacturers and found nickel on 10 of the devices.
Safety concerns
As of 2007, several airlines are experimenting with base station and antenna systems installed to the aeroplane, allowing low power, short-range connection of any phones aboard to remain connected to the aircraft's base station. Thus, they would not attempt connection to the ground base stations as during take off and landing. Simultaneously, airlines may offer phone services to their travelling passengers either as full voice and data services, or initially only as SMS text messaging and similar services. The Australian airline Qantas is the first airline to run a test aeroplane in this configuration in the autumn of 2007. Emirates has announced plans to allow limited mobile phone usage on some flights. However, in the past, commercial airlines have prevented the use of cell phones and laptops, due to the assertion that the frequencies emitted from these devices may disturb the radio waves contact of the airplane.
On March 20, 2008, an Emirates flight was the first time voice calls have been allowed in-flight on commercial airline flights. The breakthrough came after the European Aviation Safety Agency (EASA) and the United Arab Emirates-based General Civil Aviation Authority (GCAA) granted full approval for the AeroMobile system to be used on Emirates. Passengers were able to make and receive voice calls as well as use text messaging. The system automatically came into operation as the Airbus A340-300 reached cruise altitude. Passengers wanting to use the service received a text message welcoming them to the AeroMobile system when they first switched their phones on. The approval by EASA has established that GSM phones are safe to use on airplanes, as the AeroMobile system does not require the modification of aircraft components deemed "sensitive," nor does it require the use of modified phones.
In any case, there are inconsistencies between practices allowed by different airlines and even on the same airline in different countries. For example, Northwest Airlines may allow the use of mobile phones immediately after landing on a domestic flight within the US, whereas they may state "not until the doors are open" on an international flight arriving in the Netherlands. In April 2007 the US Federal Communications Commission officially prohibited passengers' use of cell phones during a flight.
In a similar vein, signs are put up in many countries, such as Canada, the UK and the U.S., at petrol stations prohibiting the use of mobile phones, due to possible safety issues.
18 studies have been conducted on the link between cell phones and brain cancer; A review of these studies found that cell phone use of 10 years or more "give a consistent pattern of an increased risk for acoustic neuroma and glioma". The tumors are found mostly on the side of the head that the mobile phone is in contact with. In July 2008, Dr. Ronald Herberman, director of the University of Pittsburgh Cancer Institute, warned about the radiation from mobile phones. He stated that there was no definitive proof of the link between mobile phones and brain tumors but there was enough studies that mobile phone usage should be reduced as a precaution. Studies are also being done on children and how mobile phone radiation affects their brains. When children start using mobile phones at a young age, they will have more years to deal with mobile phone radiation than adults will who started using mobile phones at a later age. Also, children’s brains are still developing and radiation can affect the growth of the brain easier than adults. Brains of children under 8 years of age, in fact, absorb three times the amount of radiation that adult’s brains do.
To reduce the amount of radiation being absorbed hands free devices can be used or texting could supplement calls. Calls could also be shortened or limit mobile phone usage in rural areas. Radiation is found to be higher in areas that are located away from mobile phone towers.
Etiquette
Most schools in the United States and Europe and Canada have prohibited mobile phones in the classroom, or in school due to the large number of class disruptions that result from their use, and the potential for cheating via text messaging. In the UK, possession of a mobile phone in an examination can result in immediate disqualification from that subject or from all that student's subjects. This still applies even if the mobile phone was not turned on at the time. The JCQ also requires schools to display notices of the unauthorised use of mobiles, on both the inside and outside of exam rooms. . Mobile phones can also be used for bullying and threats to other students, or displaying inappropriate material in school.
A working group made up of Finnish telephone companies, public transport operators and communications authorities has launched a campaign to remind mobile phone users of courtesy, especially when using mass transit—what to talk about on the phone, and how to. In particular, the campaign wants to impact loud mobile phone usage as well as calls regarding sensitive matters.
Many US cities with subway transit systems underground are studying or have implemented mobile phone reception in their underground tunnels for their riders. Boston, Massachusetts has investigated such usage in their tunnels, although there is a question of usage etiquette and also how to fairly award contracts to carriers.
The issue of mobile communication and etiquette has also become an issue of academic interest. The rapid adoption of the device has resulted in the intrusion of telephony into situations where it was previously not used. This has exposed the implicit rules of courtesy and opened them to reevaluation.
Use by drivers
The use of mobile phones by people who are driving has become increasingly common, either as part of their job, as in the case of delivery drivers who are calling a client, or by commuters who are chatting with a friend. While many drivers have embraced the convenience of using their cellphone while driving, some jurisdictions have made the practice against the law, such as Australia, the Canadian provinces of Quebec, Ontario, Nova Scotia, and Newfoundland and Labrador as well as the United Kingdom, consisting of a zero-tolerance system operated in Scotland and a warning system operated in England, Wales, and Northern Ireland. Officials from these jurisdictions argue that using a mobile phone while driving is an impediment to vehicle operation that can increase the risk of road traffic accidents.
Studies have found vastly different relative risks (RR). Two separate studies using case-crossover analysis each calculated RR at 4, while an epidemiological cohort study found RR, when adjusted for crash-risk exposure, of 1.11 for men and 1.21 for women.
A simulation study from the University of Utah Professor David Strayer compared drivers with a blood alcohol content of 0.08% to those conversing on a cell phone, and after controlling for driving difficulty and time on task, the study concluded that cell phone drivers exhibited greater impairment than intoxicated drivers. Meta-analysis by The Canadian Automobile Association and The University of Illinois found that response time while using both hands-free and hand-held phones was approximately 0.5 standard deviations higher than normal driving (i.e., an average driver, while talking on a cell phone, has response times of a driver in roughly the 40th percentile).
Driving while using a hands-free device is not safer than driving while using a hand-held phone, as concluded by case-crossover studies. epidemiological studies, simulation studies, and meta-analysis. Even with this information, California recently passed a cell phone law that requires drivers who are 18 years of age or older to use a hands-free device while using the phone in the vehicle. Moreover, this law also restricts drivers under the age of 18 from using a mobile phone. This law went into effect on July 1, 2008 with a $20 fine for the first offense and $50 fines for each subsequent conviction. The consistency of increased crash risk between hands-free and hand-held phone use is at odds with legislation in over 30 countries that prohibit hand-held phone use but allow hands-free. Scientific literature is mixed on the dangers of talking on a phone versus those of talking with a passenger, with the Accident Research Unit at the University of Nottingham finding that the number of utterances was usually higher for mobile calls when compared to blindfolded and non-blindfolded passengers, but the University of Illinois meta-analysis concluding that passenger conversations were just as costly to driving performance as cell phone ones.
Environmental impacts
Like all high structures, cellular antenna masts pose a hazard to low flying aircraft. Towers over a certain height or towers that are close to airports or heliports are normally required to have warning lights. There have been reports that warning lights on cellular masts, TV-towers and other high structures can attract and confuse birds. US authorities estimate that millions of birds are killed near communication towers in the country each year.
Some cellular antenna towers have been camouflaged to make them less obvious on the horizon, and make them look more like a tree.
An example of the way mobile phones and mobile networks have sometimes been perceived as a threat is the widely reported and later discredited claim that mobile phone masts are associated with the Colony Collapse Disorder (CCD) which has reduced bee hive numbers by up to 75% in many areas, especially near cities in the US. The Independent newspaper cited a scientific study claiming it provided evidence for the theory that mobile phone masts are a major cause in the collapse of bee populations, with controlled experiments demonstrating a rapid and catastrophic effect on individual hives near masts.
Mobile phones were in fact not covered in the study, and the original researchers have since emphatically disavowed any connection between their research, mobile phones, and CCD, specifically indicating that the Independent article had misinterpreted their results and created "a horror story".
While the initial claim of damage to bees was widely reported, the corrections to the story were almost non-existent in the media.
There are more than 500 million used mobile phones in the US sitting on shelves or in landfills , and it is estimated that over 125 million will be discarded this year alone. The problem is growing at a rate of more than two million phones per week, putting tons of toxic waste into landfills daily. Several companies offer to buy back and recycle mobile phones from users. In the United States many unwanted but working mobile phones are donated to women's shelters to allow emergency communication.
Usage
By civilians
An increasing number of countries, particularly in Europe, now have more mobile phones than people. According to the figures from Eurostat, the European Union's in-house statistical office, Luxembourg had the highest mobile phone penetration rate at 158 mobile subscriptions per 100 people, closely followed by Lithuania and Italy. In Hong Kong the penetration rate reached 139.8% of the population in July 2007. Over 50 countries have mobile phone subscription penetration rates higher than that of the population and the Western European average penetration rate was 110% in 2007 (source Informa 2007). Canada currently has the lowest rates of mobile phone penetrations in the industrialised world at 58%.
There are over five hundred million active mobile phone accounts in China, as of 2007, but the total penetration rate there still stands below 50%. The total number of mobile phone subscribers in the world was estimated at 2.14 billion in 2005. The subscriber count reached 2.7 billion by end of 2006 according to Informa, and 3.3 billion by November, 2007, thus reaching an equivalent of over half the planet's population. Around 80% of the world's population has access to mobile phone coverage, as of 2006. This figure is expected to increase to 90% by the year 2010.
In some developing countries with little "landline" telephone infrastructure, mobile phone use has quadrupled in the last decade. The rise of mobile phone technology in developing countries is often cited as an example of the leapfrog effect. Many remote regions in the third world went from having no telecommunications infrastructure to having satellite based communications systems. At present, Africa has the largest growth rate of cellular subscribers in the world, its markets expanding nearly twice as fast as Asian markets.
The availability of prepaid or 'pay-as-you-go' services, where the subscriber is not committed to a long term contract, has helped fuel this growth in Africa as well as in other continents.
On a numerical basis, India is the largest growth market, adding about 6 million mobile phones every month. With 256.55 million total landline and mobile phones, market penetration in the country is still low at 22.52%. India expects to reach 500 million subscribers by the end of 2010. Simultaneously, landline phone ownership is decreasing gradually and accounts for approximately 40 million connections.
There are three major technical standards for the current generation of mobile phones and networks, and two major standards for the next generation 3G phones and networks. All European and African countries and many Asian countries have adopted a single system, GSM, which is the only technology available on all continents and in most countries and covers over 74% of all subscribers on mobile networks. In many countries, such as the United States, Australia, Brazil, Canada, Costa Rica, India,, South Korea, and Vietnam, GSM co-exists with other internationally adopted standards such as CDMA and TDMA, as well as national standards such as iDEN in the USA and PDC in Japan. Over the past five years several dozen mobile operators (carriers) have abandoned networks on TDMA and CDMA technologies, switching over to GSM.
With third generation (3G) networks, which are also known as IMT-2000 networks, about three out of four networks are on the W-CDMA (also known as UMTS) standard, usually seen as the natural evolution path for GSM and TDMA networks. One in four 3G networks is on the CDMA2000 1x EV-DO technology. Some analysts count a previous stage in CDMA evolution, CDMA2000 1x RTT, as a 3G technology whereas most standardization experts count only CDMA2000 1x EV-DO as a true 3G technology. Because of this difference in interpreting what is 3G, there is a wide variety in subscriber counts. As of June 2007, on the narrow definition there are 200 million subscribers on 3G networks. By using the more broad definition, the total subscriber count of 3G phone users is 475 million.
Culture and customs
Between the 1980s and the 2000s, the mobile phone has gone from being an expensive item used by the business elite to a pervasive, personal communications tool for the general population. In most countries, mobile phones outnumber land-line phones, with fixed landlines numbering 1.3 billion but mobile subscriptions 3.3 billion at the end of 2007.
In many markets from Japan and South Korea , to Scandinavia, to Malaysia, Singapore, Taiwan and Hong Kong, most children age 8-9 have mobile phones and the new accounts are now opened for customers aged 6 and 7. Where mostly parents tend to give hand-me-down used phones to their youngest children, in Japan already new cameraphones are on the market whose target age group is under 10 years of age, introduced by KDDI in February 2007. The USA also lags on this measure, as in the US so far, about half of all children have mobile phones. In many young adults' households it has supplanted the land-line phone. Mobile phone usage is banned in some countries, such as North Korea and restricted in some other countries such as Burma.
Given the high levels of societal mobile phone service penetration, it is a key means for people to communicate with each other. The SMS feature spawned the "texting" sub-culture amongst younger users. In December 1993, the first person-to-person SMS text message was transmitted in Finland. Currently, texting is the most widely used data service; 1.8 billion users generated $80 billion of revenue in 2006 (source ITU). Many phones offer Instant Messenger services for simple, easy texting. Mobile phones have Internet service (e.g. NTT DoCoMo's i-mode), offering text messaging via e-mail in Japan, South Korea, China, and India. Most mobile internet access is much different from computer access, featuring alerts, weather data, e-mail, search engines, instant messages, and game and music downloading; most mobile internet access is hurried and short.
The mobile phone can be a fashion totem custom-decorated to reflect the owner's personality. This aspect of the mobile telephony business is, in itself, an industry, e.g. ringtone sales amounted to $3.5 billion in 2005.
Mobile phone use can be an important matter of social discourtesy: phones ringing during funerals or weddings; in toilets, cinemas and theatres. Some book shops, libraries, bathrooms, cinemas, doctors' offices and places of worship prohibit their use, so that other patrons will not be disturbed by conversations. Some facilities install signal-jamming equipment to prevent their use, although in many countries, including the US, such equipment is illegal. Some new auditoriums have installed wire mesh in the walls to make a Faraday cage, which prevents signal penetration without violating signal jamming laws.
Trains, particularly those involving long-distance services, often offer a "quiet carriage" where phone use is prohibited, much like the designated non-smoking carriage of the past. In the UK however many users tend to ignore this as it is rarely enforced, especially if the other carriages are crowded and they have no choice but to go in the "quiet carriage". In Japan, it is generally considered impolite to talk using a phone on any train -- e-mailing is generally the mode of mobile communication. Mobile phone usage on local public transport is also increasingly seen as a nuisance; the city of Graz, for instance, has mandated a total ban of mobile phones on its tram and bus network in 2008 (though texting and emailing is still allowed).
Mobile phone use on aircraft is starting to be allowed with several airlines already offering the ability to use phones during flights. Mobile phone use during flights used to be prohibited and many airlines still claim in their in-plane announcements that this prohibition is due to possible interference with aircraft radio communications. Shut-off mobile phones do not interfere with aircraft avionics; the concern is partially based on the crash of Crossair Flight 498. The recommendation why phones should not be used during take-off and landing, even on planes that allow calls or messaging, is so that passengers pay attention to the crew for any possible accident situations, as most aircraft accidents happen on take-off and landing.
By government agencies
Law enforcement
Law enforcement have used mobile phone evidence in a number of different ways. Evidence about the physical location of an individual at a given time can be obtained by triangulating the individual's cellphone between several cellphone towers. This triangulation technique can be used to show that an individual's cellphone was at a certain location at a certain time. The concerns over terrorism and terrorist use of technology prompted an inquiry by the British House of Commons Home Affairs Select Committee into the use of evidence from mobile phone devices, prompting leading mobile telephone forensic specialists to identify forensic techniques available in this area. NIST have published guidelines and procedures for the preservation, acquisition, examination, analysis, and reporting of digital information present on mobile phones can be found under the NIST Publication SP800-101.
In the UK in 2000 it was claimed that recordings of mobile phone conversations made on the day of the Omagh bombing were crucial to the police investigation. In particular, calls made on two mobile phones which were tracked from south of the Irish border to Omagh and back on the day of the bombing, were considered of vital importance.
Further example of criminal investigations using mobile phones is the initial location and ultimate identification of the terrorists of the 2004 Madrid train bombings. In the attacks, mobile phones had been used to detonate the bombs. However, one of the bombs failed to detonate, and the SIM card in the corresponding mobile phone gave the first serious lead about the terrorists to investigators. By tracking the whereabouts of the SIM card and correlating other mobile phones that had been registered in those areas, police were able to locate the terrorists.
Disaster response
The Finnish government decided in 2005 that the fastest way to warn citizens of disasters was the mobile phone network. In Japan, mobile phone companies provide immediate notification of earthquakes and other natural disasters to their customers free of charge . In the event of an emergency, disaster response crews can locate trapped or injured people using the signals from their mobile phones. An interactive menu accessible through the phone's Internet browser notifies the company if the user is safe or in distress. In Finland rescue services suggest hikers carry mobile phones in case of emergency even when deep in the forests beyond cellular coverage, as the radio signal of a cellphone attempting to connect to a base station can be detected by overflying rescue aircraft with special detection gear. Also, users in the United States can sign up through their provider for free text messages when an AMBER Alert goes out for a missing person in their area.
However, most mobile phone networks operate close to capacity during normal times and spikes in call volumes caused by widespread emergencies often overload the system just when it is needed the most. Examples reported in the media where this have occurred include the September 11, 2001 attacks, the 2003 Northeast blackouts, the 2005 London Tube bombings, Hurricane Katrina, the 2006 Hawaii earthquake, and the 2007 Minnesota bridge collapse.
Under FCC regulations, all mobile telephones must be capable of dialing emergency telephone numbers, regardless of the presence of a SIM card or the payment status of the account.
See also
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