Android is the name of the Linux based operating system that is backed by Google and the other members of the Open Handset Alliance. Because of Android's open source nature, Android based smart phones should be cheaper to produce than those that use operating systems, such as Microsoft's Windows Mobile, that require a royalty fee be paid for each use. The T-Mobile G1, announced on September 23, 2008, was the first Android OS smart phone to be officially introduced to the market.

iOS (formerly iPhone OS) is Apple Inc.'s mobile operating system. Originally developed for the iPhone, it has since been extended to support other Apple, Inc. devices such as the iPod Touch, iPad, and Apple TV. Apple does not license iOS for installation on non-Apple hardware. As of October 4, 2011, Apple, Inc.'s App Store contained more than 500,000 iOS applications,[3] which have collectively been downloaded more than 18 billion times.

Symbian is a mobile operating system (OS) and computing platform designed for smart phones and currently maintained by Accenture.[7] The Symbian platform is the successor to Symbian OS and Nokia Series 60; unlike Symbian OS, which needed an additional user interface system, Symbian includes a user interface component based on S60 5th Edition. The latest version, Symbian^3, was officially released in Q4 2010, first used in the Nokia N8. In May 2011 an update, Symbian Anna, was officially announced, followed by Nokia Belle (previously Symbian Belle) in August 2011.[8][9]

Windows Mobile is a mobile operating system developed by Microsoft for smart phones and Pocket PCs,[2]. It is based on the Windows CE kernel and first appeared as the Pocket PC 2000 operating system. It is supplied with a suite of basic applications developed with the Microsoft Windows API, and is designed to have features and appearance somewhat similar to desktop versions of Windows. Third parties can develop software for Windows Mobile with no restrictions imposed by Microsoft. Some software applications can be purchased using Windows Marketplace for Mobile.