Earlier this week when the Zune software was updated to version 4.7 to get ready for Windows Phone 7 I mentioned on Twitter that a Twitter app was missing from the Zune Windows Phone App Marketplace.
Well although it may not be in the Zune Marketplace yet that does not mean that Twitter functionality is not available on the Windows Phone 7 handsets.
Check out this Channel 9 video demo of a Twitter app on a HTC Windows Phone:
The only thing I am unsure of is if this is a built in app on the HTC handset or is part of Windows Phone 7 itself.
More to follow on that question.