Something to be aware of if you Lync \ OCS Federate with Microsoft

The federated edge server that supports Instant Messaging and conferencing with external companies will be migrated to Microsoft Lync Server 2010 on Friday, March 18, 2011.

After the server migration, the IP address for the microsoft.com SIP domain will change to 65.55.130.30. External companies who are federated with Microsoft may need to make changes to their infrastructure outlined in Instructions below in order for the federation to continue to function successfully.

http://blogs.technet.com/b/nexthop/archive/2011/03/08/microsoft-federated-edge-server-ip-address-change-march-11-2011.aspx