The eXtensible Messaging and Presence Protocol (XMPP) Gateway for Office Communications Server allows Office Communications Server users to communicate with users who use an XMPP-based IM and presence provider such as Google Talk and Jabber. Once the gateway is deployed in an Office Communications Server environment, users hosted on Office Communications Server can do the following:

• Add or delete users on an XMPP environment as contacts
• Communicate with users on XMPP environment through one-on-one IM conversations.

Download & documentation:
http://www.microsoft.com/downloads/details.aspx?FamilyID=aa560bfe-9960-473a-bfb8-53bff678cec4&displaylang=en