Hello,
Yes, you can do this. At this moment I believe you will need a 2nd server as a mediation server to go between OCS and the SIP/PSTN Gateway. I have been researching and understand that you can go direct now. (i'm checking one server possibility)
There are several phone handsets becoming available: Polycom has one. SNOM recently released an OCS edition of their SNOM 3XX handset that are a very reasonable price.
matt
landiscomputer