What method are you using to transfer a caller to a particular mailbox? If the user simply does a quick release transfer to the Unity pilot number then the Nortel will present this a direct call, and so Unity will play either the opening greeting or a sign-in prompt. This certianly isn't what you want.
To direct the transfer to a particular mailbox I suspect you are doing one of two things, either 1) transfer to an extension that is set to forward to voicemail (this extension number would then be the extension or alternate extension of the desired mailbox) or 2) transfer to the opening greeting then dial the mailbox extension followed by #2 before releasing the transfer. Or are you doing something else?
In case 1, you could achieve what you want, but as you've noticed it relies on the user releasing the transfer before the call info is sent to Unity. If releasing the transfer quicker is not possible, you'll need to find a way to slow down the call info to Unity. e.g. can a forwarding delay be added on the Nortel?
In case 2, there really is no way to achieve what you're after. The Nortel will always present the call to Unity as a direct call from the transfering user. This is what Unity will use as caller ID for the call.
Regards,
Eric
