KB 956389 - Office Communications Server 2007: November 2008 - mostly for interop between R1 and R2

This update package fixes the following issues:

KB 958560 - When a Communicator 2007 user calls a Conference Auto Attendant access number, the call always uses Mediation Server instead of going to the Conference Auto Attendant directly

KB 958561 - Communications Server 2007 R2 remote users cannot make public switched telephone network (PSTN) calls when Communications Server 2007 servers or proxies are in the call path

Although not well documented yet, you will need to the October 2008 Communicator update to be able to interact with OCS 2007 R2 servers and users.