Microsoft has yet to clarify the exact release date of Windows Phone 7 Mango, that is, when those with WP7 hardware can expect an OTA update to bring the new operating system to their device. WPCentral is citing three pieces of evidence that point to a September 15 release date for Mango. First, a well-known app firm has told them that indeed, September 15 is the day. Second, a chat with a customer service rep from HTC reveals that September is going to be the month, but that a firm date could not be given. And third, the acclaimed Dell Venue Pro which has been unavailable in the AT&T flavor for quite some time, is now showing a shipping date of September 16, presumably so that it’ll be able to ship with the Mango update.