The default port range used by Office Communicator R2 is 1024-65535 over both TCP & UDP. Each peer connection will negotiate communications over multiple dynamic ports in that range.
Because this port range is so large, when allowing for peer connections through firewalls you can reduce the range by configuring specific registry keys on the computers with Office Communicator deployed: http://technet.microsoft.com/en-us/library/dd425164(office.13).aspx
The Portrange values should not be reduced to any less than 40 total ports for correct connectivity, but using a range of any more than 40 doesn't offer any performance benefits. That smaller range would be much easier to allow on firewalls.
Jeff Schertz, PointBridge | MVP | MCITP: Enterprise Messaging | MCTS: OCS