Microsoft is sending out invites to a Windows Phone preview party in New York and we just got ours. On May 24, 2011 Microsoft will "lift the curtain on the next major release of Windows Phone". A similar event will be held on the same date in London.
As more information becomes available on this event, we'll keep you posted. We're also planning on covering the event and will pass on all the details on the next major release of Windows Phone.