Using CCA?
Phone will auto register, but no auto ephone-dn assignment, hence the blank screen, most likely (only the system message in lower left, correct)?.
If thats the case, check in CCA, and I think you may see the phones waiting to be assigned. After you do, the phone should reset as a new endpoint, and then you will have the joy of transfering the information.
If they are different models, with different button capabilities, it may not work to swap MAC addresses, but that is the case where to get a MAC to 'unregister" from CME, the reboot will do that (as long as the old phone is unplugged at that point.
I realize this is confusing to follow and apologize in advance.