It was officially launched back in May, but the availability date for the Windows Phone 7 Mango was vaguely pinned to autumn. However, rumours now suggest that the update will come through on a more specific date – 1 September.That's according to Pocket-lint, which claims confirmation of the same September date from 'multiple trusted sources'. That would be perfect timing ahead of the IFA trade show in Berlin, which starts a day later. Microsoft could launch a clutch of handsets packing the OS upgrade to capitalise on it. It would certainly make a lot of sense. Good timing ahead of that first Nokia Windows Phone 7 handset too.When we got up-close with Mango earlier in the summer, we found a version of WP7 with an improved browser, support for more social features and quite simply, a more rounded package. Specifically, things like a contacts book, already with Facebook contact, photo and status sync, now with Twitter and LinkedIn support too. Also, there was a new Threads feature showing communication with a particular friend across IMs, email and text. You can also put your friends into groups, which you can view from a single home screen.Mango will offer a new, desktop-like Internet Explorer 9 browser, including local search functionality, as well as a wider selection of apps – up to 18,000 by the time the update launches. As we said, that should be in a matter of weeks, free to all existing users.