This project develops a third-party plugin for the Pidgin  multi-protocol
instant messenger. It implements the extended version of SIP/SIMPLE used by
various products:

* Microsoft Office Communications Server (OCS 2007/2007 R2 and newer)
* Microsoft Live Communications Server (LCS 2003/2005)
* Reuters Messaging

With this plugin you should be able to replace your Microsoft Office
Communicator client with Pidgin.