When Troubleshooting Exchange UM and RNL (reverse number lookup) Jens has a blog on how Exchange behave and Glen has a blog regarding diagnostic logging.
Then key takeaways in Jens blog on Exchange and RNL, is that Exchange UM use the Active Directory attribute msRTCSIP-Line and personal contacts for RNL.
When you need to troubleshoot Exchange UM you set the Loglevel on Exchange UM with Glen’s Powershell script and then you will get all the “debug like” information in the eventlog on Exchange
Event log Category: get info here
Jens blog on Exchang UM here