Microsoft, seeking to tap into the rapidly growing smartphone market, announced on Tuesday that new cellphones coming in October will feature an upgraded mobile operating system.

The Redmond, Washington-based software giant said mobile phones from its handset partners hitting stores on 6 October will be the first to feature Windows Mobile 6.5, the latest version of its mobile phone software.

The new phones, to be branded as "Windows Phones," will feature a redesigned web browser and a free service called "My Phone," which allows users to back up contacts, messages and photos on a personal computer or the internet.

Microsoft also announced plans to launch an online applications store ? Windows Marketplace for Mobile ? like Apple's popular App Store for the iPhone or Research in Motion's recently unveiled Blackberry App World.

It said a "wide variety" of applications will be available for the devices to be offered by hardware manufacturers in North America, Europe, Latin America and the Asia-Pacific region.

Other features include email using Microsoft Office Outlook Mobile and Microsoft Office Mobile, which allows users to open and edit Word, Excel and PowerPoint documents from their phone.

Microsoft's share of the market for smartphone operating systems fell to nine percent in the second quarter from 12 percent a year ago, according to research firm Gartner.

Nokia's Symbian is the leader with a 51 percent share of the market according to Gartner, while RIM commands around 21 percent and Apple has increased its share to 13.3 percent from 2.8 percent a year ago.

Google's open-source Android mobile phone software is another new entry in the operating system space and the internet giant has carved out a two percent market share.

While worldwide mobile phone sales fell 6.1 percent in the second quarter, smartphone sales increased by 27 percent in the period to 40.9 million units, according to Gartner.