Sounds like you have VOIP and this is at work. If so, the Avaya handset is analogous to a PC. That is, it has an IP address and that address is tied into a network port. First, you can try getting the old and new port address off the wall jacks. Go into the telephone closet and locate the phone switch and patch panel. The port address at the switch and panel should match those addresses at the wall jack. Simply patch the cable from the old port address to the new port address at the telephone switch. Most organizations have IT folks that will do this for you.
