Well I will admit, I have a 9630G working on a non Avaya SIP platform. It's from a hosted provider called VOIP.MS.
The ring tones, call quality, cool looking phone design and some features make it great, BUT I do not have access to the ton of cool features that an Avaya platform would offer.
It operates like a basic digital phone, you can transfer, conference, park, page, pickup, and forward, but you cannot use advanced Avaya features such as presence or Rich Ring tones. You also cannot program buttons, nor use a MWI light for messages unless connected to an Avaya server.
If you are looking for a good SIP phone to use on Asterisk, I'd suggest the a Cisco 79xx or Nortel 11xx/12xx SIP set.
"Keep the Peace, Use RLS"