A telephone number or phone number is a sequence of digits used to call from one telephone line

Telephone line

A telephone line or telephone circuit is a single-user circuit on a telephone communication system...

 to another in a public switched telephone network

Public switched telephone network

The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...

. When telephone numbers were invented, they were short — as few as one, two or three digits — and were given orally to a switchboard operator

Switchboard operator

In the early days of telephony, through roughly the 1960s, companies used manual telephone switchboards and switchboard operators connected each call by inserting a pair of phone plugs into the appropriate jacks. Each pair of plugs was part of a cord circuit with a switch associated that let the...

. As phone systems have grown and interconnected to encompass the world, telephone numbers have become longer. In addition to telephone

Telephone

The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

s, they now access other devices, such as computers and fax machines.

The number contains the information necessary to identify uniquely the intended endpoint for the telephone call

Telephone call

A telephone call is a connection over a telephone network between the calling party and the called party.-Information transmission:A telephone call may carry ordinary voice transmission using a telephone, data transmission when the calling party and called party are using modems, or facsimile...

.