Microsoft is planning to release Windows Phone Mango to developers on Thursday.
The software giant will make beta copies of Windows Phone Mango available to registered Windows Phone Developers according to sources familiar with the company’s plans that spoke to WinRumors. Microsoft has been working to ensure the beta bits are safe for retail devices and will offer them on the company’s AppHub developer site. Windows Phone Developers pay $99 per year for access to the AppHub.
Microsoft’s Senior Director of Communications, Bill Cox, hinted at the announcement in a Twitter message on Wednesday:

Bill Cox Twitter message
Windows Phone Mango, the codename for what is expected to be labeled Windows Phone 7.5, will be released in full later this year. The update includes a number of new enhancements to existing features and tighter communications integration. Windows Phone Mango users will be able to access Facebook Chat and Windows Live Messenger services directly from the messaging hub of Windows Phone. Microsoft previously revealed that Mango contains 500 new features, including an updated version of Internet Explorer to support HTML5 content.