Avaya 4602

Anyone use an Avaya 4602 with Asterisk? I have mine running the latest SIP firmware, and it works well, except for a few nagging bits…
Particularly, does anyone know how to tell it what the Asterisk voicemail extension is, so that the message button will dial it?
There’s a MSGNUM setting in the 46xxsettings.txt file, but that only works for 9600-series phones.

Many thanks in advance!