Skagen

Zune Phone: Implications for Microsoft's Mobile Partners

HTC makes the vast majority of Windows Mobile phones (under a variety of brands) and they have been pushing VOIP in phones, so clearly they are onboard with the idea of bypass the traditional phone business. This functionality could - and probably would - simply be thrown in with their devices.

And I'll bet you HTC would be the one who would actually make this phone for MS in any case. They are more or less MS's phone arm.