On the Microsoft TechNet website, Microsoft has collected all the certified devices for OC 2007 & OC 2007 R2
Phones and Devices Optimized for Microsoft Office Communicator:
We can expect some new releases of devices after MS puts R2 on the street. I have heard Polycom will be improving the CX200 USB handset with a NUM pad.
Watch the TechNet website (or this blog) for udates on new devices.