Have you had any luck solving this issue? I am having the exact same problem. What I have found is that the local provider is saying that the number is not coming across in E.164 format which then appears to them as an unknown number so they just append either the main phone number to the caller ID or sometimes the phone number associated with billing contact. The nortel works just fine in both senarios, but there seems to be something lost in translation between the Cisco and Nortel. So far I haven't been able to find a setting to fix this.
... View more