According to this video of a Microsoft Live Labs presentation of Windows Phone 7 at Cannes Lions 2010, Windows Phone 7 will be coming this October. Listen yourself, the month slips out around the :16 mark. [Thanks, Gary!]
Don't under estimate the power of Mobile Sharepoint, Mobile Office, and better Exchange integration. Not to mention Xbox Live integration and Zune pass compatibility.
There is just enough new (read as not supported by other phones) features in this phone to warrant a possible shift in the mobile landscape.
Add to that, it will be on every carrier with tons of hardware manufacturers.
I think this will be the nail in Blackberry's coffin for business, and a more capable, less buggy/fragmented alternative to iPhone than Android is.
Full disclosure: I have a Macbook Pro and a Droid Eris, and am a Senior Systems Engineer for a major enterprise business solutions firm in Dallas, TX.