The most common operating systems (OS) used in smartphones by Q2 2009 sales are:

Symbian OS from the Symbian Foundation (50.3% Market Share Sales Q2 2009)
Symbian has the largest share in most markets worldwide, but lags behind other companies in the relatively small but highly visible North American market. This matches the success of its largest shareholder and customer, Nokia, in all markets except Japan. Nokia itself enjoys 52.9% of the smartphone market. In Japan Symbian is strong due to a relationship with NTT DoCoMo, with only one of the 44 Symbian handsets released in Japan coming from Nokia. It has been used by many major handset manufacturers, including BenQ, Fujitsu, LG, Mitsubishi, Motorola, Nokia, Samsung, Sharp, and Sony Ericsson. Current Symbian-based devices are being made by Fujitsu, Nokia, Samsung, Sharp, and Sony Ericsson. Prior to 2009 Symbian supported multiple user interfaces, i.e. UIQ from UIQ Technologies, S60 from Nokia, and MOAP from NTT DOCOMO. As part of the Symbian Foundation Platform in 2009 these three UIs were merged into a single platform which is due to be fully open source by mid 2010. It has received some adverse press attention due to virus threats (namely trojan horses).

RIM BlackBerry OS (20.9% Market Share Sales Q2 2009)
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. (13.7% Market Share Sales Q2 2009)
The iPhone uses an operating system called iPhone OS, which is derived from Mac OS X. Third party applications were not officially supported until the release of iPhone OS 2.0 on July 11th 2008. Before this, “jailbreaking” allowed third party applications to be installed, and this method is still available.

Windows Mobile from Microsoft (9% Market Share Sales Q2 2009)
The Windows CE operating system and 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 Standard, were unveiled in February 2007. Windows Mobile benefits from the low barrier to entry for third-party developers to write new applications for the platform.[citation needed] It has been criticized for having a user interface which is not optimized for touch input by fingers; instead, it is more usable with a stylus. However, unlike iPhone OS, it does support both touch screen and physical keyboard configurations. With next major release of Windows Mobile, Windows Mobile 7, Microsoft intends to make a dramatic come-back in the industry and become a much more aggressive force in the mobile space than it has been before in the past.

Android from Google Inc. (2.8% Market Share Sales Q2 2009)
Android was developed by Google Inc.. Android is an Open Source, Linux-derived platform backed by Google, along with major hardware and software developers (such as Intel, HTC, ARM, and eBay, to name a few), that form the Open Handset Alliance. This OS, though very new, already has a cult following among programmers eager to develop apps for its flexible, Open Source, back end.Android promises to give developers access to every aspect of the phone’s operation. This lends many to foresee the promise of further growth for the Android platform.

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 Android, LiMo, Maemo, Openmoko and Qt Extended, 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 webOS from Palm Inc. and Palm OS/Garnet OS from Access Co.
Palm webOS is Palm’s next generation operating system. 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.

bada from Samsung Electronics
The bada mobile phone operating system is still in development, and Samsung expects handsets to be available in the second half of 2010.

Maemo from Nokia
Maemo is a software platform developed by Nokia for smartphones and Internet Tablets. It is based on the Debian operating system.

Maemo is mostly based on open source code, and has been developed by Maemo Devices within Nokia in collaboration with many open source projects such as the Linux kernel, Debian and GNOME.

Maemo is based on Debian GNU/Linux and draws much of its GUI, frameworks and libraries from the GNOME project. It uses the Matchbox window manager and the GTK-based Hildon as its GUI and application framework.