Information on the 7920 is at:
formatting link
Note that it runs SCCP (a "Skinny" proprietary version of H.323
developed by Selsius - who was bought by Cisco a few years ago).
Cisco and Asterisk (maybe others?) support this protocol for
registering phones.
The quickest way to get the phone running is to follow the SCCP link
on the above web page. Essentially, you need to install Asterisk on a
machine in your network and register the phone to it. At that point
you will have dialtone, and can trans-code out to IAX, SIP, H.323 or
even POTS. :-)
HTH,
JDB