If you can connect a line to the Pbx, Avaya might be able to dial into the system and reset the password for u. If it was installed at another location then that information might help. The old passwords that Avaya has in their data base might be on the records for the old location. But it wouldn't be your passwords, just theirs to go in and reset yours. I believe that Avaya can decode passwords from tapes or flash cards, but I am not sure of that. They are going to charge u even if u have maint on the system through Avaya. (yes, believe it or not, some people have maint on systems in storage.)
If u bought the stored PBx from someone else, I have been told that u bought only the hardware. To use the Pbx legally u have to buy the software from Avaya again. If u bought a whole company that owned the pbx, then u have rights to the software too. That is what I have been told.