You need a 355A adapter to connect to the serial port, you can google the pinout. It's not a Cisco console cable, but you can make an adapter to get that going. I seem to remember 19200-N-8-1, but you can just change baud rates until it answers you when you press enter.

You can also use a modem and dial into the auto attendant and transfer to the onboard mpdem.

The programming software is on the avaya support site, or I can send you a link to it on my site.

The gui is great for making a lot of mailboxes at once, and for troubleshooting things like outcalling.