While we know that Microsoft is working with Nokia on the Finish company's first Windows Phone Mango smartphone, neither Microsoft nor Nokia have so far confirmed anything in terms of a planned release date. All we have seen so far are leaked videos of the Nokia Sea Ray. However, following KDDI's earlier announcement to launch the first Mango smartphone anytime August in Japan, it seems Nokia and Microsoft are also preparing something for August. Both companies have just sent out an invitation for a joint-event at this month's GamesCom in Cologne, Germany. According to the invitation, attendees can expect "exciting actions and surprises", which "will make it an an evening to remember".
Furthermore, Nokia and Microsoft will raffle 3 Nokia (phones) with Windows Phone (as soon as available) so it sounds like the 17th could be the official announcement date but not the sales start of Nokia's first Windows Phone 7 smartphone.
UPDATE: As of yesterday, we've received further information and according to them, it's not a launch event at all but should engage (games) developers to the Windows Phone platform as well as to Nokia and Microsoft. It wasn't confirmed that there won't be a Nokia Windows Phone on some kind of display but I could imagine anyway that Nokia might give a first public sneak-peek anyway.
Cheers ~ Arne