We've done it and it works very well.
We even created a technical step by step document
Looking at your profile picture you may be local to us and a direct competitor so i'm not sure I should pass it on
Any chance you would like to share this document? I would like a copy but the preferred method would be to start a new thread that we would sticky in the 5000 area like this:
[HOWTO] 5000 SIP Networking to Avaya IP Officethen that becomes the thread for all discussions related to that topic.
Side note here: I get a little frustrated with PBX forums in general in this area, there is no organization, FAQ, sticky threads with pointer info, ect, like most Android or other ujser support forums have... just need to start somewhere.