Microsoft will begin rolling out Windows Phone 7.5 “Mango” to last year’s Windows Phone lineup beginning September 1st, Pocket-lint reports. The British tech blog cites multiple trusted sources with its report, and it says September 1st will also mark the start of device announcements touting Microsoft’s Mango OS. The date just one day ahead of this year’s IFA trade show in Berlin, where Pocket-lint says Microsoft may have Windows Phone 7.5-powered devices on display alongside manufacturers like Samsung ZTE and LG. Nokia is not expected to unveil its first Windows Phone until its annual Nokia World event in October. Microsoft’s Joe Belfore addressed the rumor without confirming or denying it early Friday morning, saying only that it is, in fact, a rumor.