Hi Tom,
Try to see on the AC gateway in a trace of an inbound call if the calling line id (from) field is populated at that stage. My guess is that it is already missing at this point in the chain. If it's there you could try to trace on the mediation server.
OCS and OC shouldn't display anonymous unless it is anonymous/missing from the begining. If there is a number it should display the number or do reverse number lookup on your contacts, Outlook contacts and AD.
best regards
Jens