The Palm Treo ˈtriːoʊ is a line of smartphone

Smartphone

A smartphone is a high-end mobile phone built on a mobile computing platform, with more advanced computing ability and connectivity than a contemporary feature phone. The first smartphones were devices that mainly combined the functions of a personal digital assistant and a mobile phone or camera...

s originally developed by Handspring

Handspring (company)

Handspring was a maker of Palm OS-based Visor- and Treo-branded personal digital assistants. It was run by Jeff Hawkins, Donna Dubinsky, and Ed Colligan, the original inventors of the Palm Pilot and founders of Palm Computing, after they became unhappy with the direction in which 3Com was taking...

, which was bought by Palm, Inc.

Palm, Inc.

Palm, Inc., was a smartphone manufacturer headquartered in Sunnyvale, California, that was responsible for products such as the Pre and Pixi as well as the Treo and Centro smartphones. Previous product lines include the PalmPilot, Palm III, Palm V, Palm VII, Zire and Tungsten. While their older...

 They are now manufactured and maintained by Palm, Inc. Treos have a number of integrated features such as the ability to check the calendar while talking on the phone, dial directly from a list of contacts, and send email messages. Recent models include a built-in camera. Traditionally, Treos run Palm OS

Palm OS

Palm OS is a mobile operating system initially developed by Palm, Inc., for personal digital assistants in 1996. Palm OS is designed for ease of use with a touchscreen-based graphical user interface. It is provided with a suite of basic applications for personal information management...

 which allows synchronization with both Mac OS X

Mac OS X

Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

 and Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

, but newer models also have editions that run Windows Mobile

Windows Mobile

Windows Mobile is a mobile operating system developed by Microsoft that was used in smartphones and Pocket PCs, but by 2011 was rarely supplied on new phones. The last version is "Windows Mobile 6.5.5"; it is superseded by Windows Phone, which does not run Windows Mobile software.Windows Mobile is...

.
As of August 2008, there have been nineteen Treo models, listed below in order of release.