Using the OCS Management Console expand out to the pool object (not the server itself) and right-click and goto Properties > Front-End Properties. Change to the Voice tab and then under Location Profile select which location profile you want to be assigned as deafult to the users homed on that server/pool. If you went through the Exchange UM Integration steps then you should have an entry that looks something like "profilename.domain.com".
Here are the official instructions for this step:
http://technet.microsoft.com/en-us/library/dd425328(office.13).aspx
Jeff Schertz, PointBridge | MVP | MCITP: Enterprise Messaging | MCTS: OCS