[Serusers] cisco phone domain

Hi, We've just installed ser we've noticed that when placing a call from a Cisco IP phone the "From:" is set to "username(a)serserver.domain.com" rather than the expected "username(a)domain.com".com". Other SIP clients (we've tested with MS Messenger) don't exhibit this problem. At first we thought ser was re-writing this, but ngrep revealed that to not be the case (the phone was actually sending this information). Inserting "rewritehost("domain.com")" into the config didn't seem to alter this any. The phone is configured with the hostname serserver.domain.com as the SIP server. Any idea why this is happening? (Apologies for the skimpiness of the details; I can follow up with config information, models, etc, but I was hoping someone had seen this before and had an idea). -- Dan