Hey there, I'll start with an overview of a transfer call flow. Suppose PhoneA calls PhoneB and then PhoneB transfers the call to PhoneC. During the transfer, A is placed on hold and B initiates a new call (consultation call) to C. For this consultation call, B is the calling party and hence C is expected to see the B's number in the display. Once B releases the transfer, A and C will be connected. At this time, C's display should be updated to show A's number.
Now, in you case I believe A is the outside caller, B is the voicemail AA, and C is the subscriber's ip phone. I think the only thing you could do to get A's number on C's display quicker would be to select blind transfers rather than supervised. If you are already using blind transfers, then I don't know of anything you can do to improve the behavior.
Regards,
Eric
