Pidgin plugin for MS Office Communicator and MS Lync

 A third-party plugin for the Pidgin multi-protocol instant messenger.
 It implements the extended version of SIP/SIMPLE used by various products:
 .
     * Microsoft Lync Server 2010
     * 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.