Windows Phone 7.5 (codenamed 'Mango') is a major software update for Windows Phone, the mobile operating system by Microsoft. Although the OS internally identifies itself as version 7.1, it is marketed as version 7.5 in all published materials intended for end-users. The update was formally announced in New York on May 24, 2011, when Microsoft gave an in-depth preview of the update, shortly before which Steve Ballmer had disclosed that there would be over 500 features.
Microsoft started rolling out Windows Phone 7.5 to both the United States and International markets on September 27, 2011. The first phones that will come pre-loaded with Windows Phone 7.5 have been slated for release sometime in the fall and/or winter 2011.