Ars Technica: "The recent receipt by AT&T stores of marketing materials that mention Windows Phone 7 has led some to speculate that it could arrive sooner still—any time between July 24, when the AT&T stores will refresh their signage, and September.
This seems unlikely, as the software still isn't ready. Microsoft wants to give developers access to Windows Phone 7—both the software and test hardware—ahead of the launch, to ensure that there are plenty of good applications available on release day. This still hasn't happened. Nor have the development tools even hit beta: the most recent release was in April, and was merely a preview."