Microsoft has granted developers an advanced look at the new Mango version of its Windows Phone operating system ahead of a wider public release.

Earlier this week, Microsoft announced that registered developers in 23 countries were offered the chance to update their handsets to a beta version of the system.

Those wishing to develop apps for the Mango build 7661 will first have to update their software development kit (SDK) to Windows Phone SDK 7.1 Beta 2.

Developers wanting to work on for the Mango build 7661 will first have to update their SDK to Windows Phone SDK 7.1 Beta 2.

Mango is the first update since the reasonably well received Windows Phone 7 platform was released over eight months ago. Officially going by the moniker Wondows Phone 7.5, it will introduce over 500 new features, concentrating on improvement in three key areas, communications, apps and the internet.

A number of new features include the ability to create contact groups, enabling targeted group messaging and group email threads. Also, the update includes a new search tool called Bing Vision, a new voice-to-text function and enhanced app multitasking.

Also, by enabling the App Connect Feature, developers can have their aps appear in search results when users perform searching using Bing.

Windows Phone 7.5 will be available on new handsets this autumn, though it is currently unclear as to when existing customers might be able to upgrade their handsets.