Also i found this it may not be your problem but it is worth a look
An issue has been identified with Nortel software release 25.10 that affects integration on all Lucent Technologies messaging products using set emulation for integration.
At NT release 25.10, the called party display information is not presented and integration is lost. This occurs when calls are transferred to extensions that are busy call forwarded, or all calls forwarded to voicemail.
An example is described below:
Calls presented to an auto-attendant that are transferred to an extension that is either busy call forwarded, or all calls forwarded to voice mail do not have the called party display information, and loss of integration occurs. Inside callers are prompted for their own password and outside callers get the system greeting.
SOLUTION:
Nortel has developed the following patch that corrects the problem: MPLR 12969
Any site that is using set emulation for integration, and is at Nortel release 25.10 should have the Nortel patch installed on the PBX.