Neowin has reason to believe from their sources that the Mango/Windows Phone 7.5 SDK will in fact be released for developers at some point today. The SDK is expected to release alongside the UK/US unveiling of the consumer based features. This initial SDK release will be a Beta so it is not final build.
Also coming from Neowin’s sources, there will be an announcement on the official release of Mango today, and it is expected to land as soon as September. Neowin updated their article as well with this clarifying statement:
Update: When we say “September release,” we’re hearing that Microsoft will release it to all carriers before then and plans on attempting some sort of unified release.
Although today’s event is a preview event, sources claim that the Mango build shown today will be the RTM build. RTM build is Release To Manufacturing, meaning that it’s the build that will be sent to device manufacturers for their devices.
Microsoft is also expected to announce an invite only preview program of Mango for developers that will either allow them access to test devices, or even flash their own phones with a release of Mango.
We just have to wait and see what Microsoft pulls out of the hat today, it seems they really are full steam ahead now with this update if all this information is true. Be sure to watch the event live at 10:00 AM EDT today.