Hi Mazilo,
I think you're barking up the wrong tree.
whereas H.323 (as supported by Opal) is an ITU Standard and is a binary protocol.
There's a tiny bit of a historical protocol overlap in that both Messenger (old, now defunct versions?) and H.323 clients (like MS Netmeeting) have used T.120 for app sharing but even then, AFAIK, they have never been interoperable for any kind of call signalling.
To my knowledge, the only major "chat" program with a large user base that uses anything close to kind of open standard is gtalk (which uses XMPP)
Hth,
Rhosyn