Ilse has a great post on how she configured the integration between Exchange 2010 SP1 OWA and Microsoft Lync Server 2010. Her lab configuration had the Exchange 2010 SP1 CAS server role co-located with HUB and MBX, but not co-located with the UM role.
If you have a slightly different configuration (like me), where the CAS and UM roles are co-located there is a small catch to following the steps Ilse outlines (in fact it is having the roles co-located on the same server and having created integration between Exchange UM and Lync Server using a SIP UM dial plan hosted by the UM server) .
The catch is that you’ll see an Error event being logged by LS Protocol Stack (event ID 14563) upon RTCSRV start, where it is basically complaining about having two entries in the known server table with different version numbers. You’ll see one entry with the role ‘Application Server’ and version 5 and another entry with role ‘Authorized Host’ and version 0. The entry with role ‘Application Server’ comes from the outcome of running New-CsTrustedApplicationPool & New-CsTrustedApplication. The entry with role ‘Authorized Host’ comes from the ExUMRouting component in Lync Server, which creates these entries for all Exchange UM Servers it finds in Active Directory hosting SIP UM dial plans.
You can safely ignore the error event, since shortly after the error event you’ll see an information event (ID 14493 from LS Protocol Stack) adding the entry with role ‘Application Server’ to the known servers table.
If you want to get rid of the error event you can remove the CsTrustedApplication representing Exchange OWA. However remember to add it back again, if you one day separate the CAS and UM role or move the SIP UM dial plan(s) to be hosted by another UM server.