Microsoft: Save the date for an October 11th event in London
Presenting WP7 in Europe first makes sense, as that's where the scheduled initial launch is, on October 21st. The US is coming hot on the heels soon after that, on November 8th. The first Windows Phone 7 handsets should appear on Vodafone in Europe, and AT&T in the States from manufacturers such as LG, HTC, Samsung, and a few others.
The keynote presentation is shaping to be rather long - 9am ET (2pm GMT) until 12:30pm (5:30pm GMT), but it could be sweet.