Symbian OS from Symbian Ltd.
Symbian has the largest share in most markets worldwide. It is used by many major handset manufacturers, including BenQ, LG, Motorola, Samsung, and Sony Ericsson. Various implementations of user interfaces on top of Symbian (most notable being UIQ and Nokia's own S60) are incompatible, which along with the requirement that applications running on mobile phones be signed is hindering the potential for a truly widely accepted mobile application platform. It has received some adverse press attention due to virus threats (actually trojan horses).



Windows Mobile from Microsoft
Windows CE operating system along with Windows Mobile middleware are widely spread in Asia. The two improved variants of this operating system, Windows Mobile 6 Professional (for touch screen devices) and Windows Mobile 6.1 Standard were unveiled in 2008. Windows Mobile is enjoying great popularity because of the low barrier to entry for third-party developers to write new applications for the platform.



RIM BlackBerry operating system
This OS is focused on easy operation and was originally designed for business. Recently it has seen a surge in third-party applications and has been improved to offer full multimedia support.



iPhone OS from Apple Inc.
The iPhone (and iPod touch) use an operating system called iPhone OS, which is derived from Mac OS X. Third party applications were originally only made available for iPhone users through a web service that can be accessed via the included web browser; however, with the release of iPhone OS 2.0 on July 11th 2008, native applications are now available and can be downloaded through the iTunes App Store.



Linux operating system
Linux is strongest in China where it is used by Motorola, and in Japan, used by DoCoMo.[Rather than being a platform in its own right, Linux is used as a basis for a number of different platforms developed by several vendors, including Motorola and TrollTech, which are mostly incompatible. PalmSource (now Access) is moving towards an interface running on Linux. Another platform based on Linux is being developed by Motorola, NEC, NTT DoCoMo, Panasonic, Samsung, and Vodafone.



Palm OS developed by PalmSource
PalmSource traditionally used its own platform developed by Palm Inc. Access Linux Platform (ALP) is an improvement that was planned to be launched in the first half of 2007. It will use technical specifications from the Linux Phone Standards Forum. The Access Linux Platform will include an emulation layer to support applications developed for Palm-based devices.