This might be of interest to the OBi devs since the Obi unit incorporates the standards of both protocols. Obihai, you may even like to participate in the Draft as you have developed an expertise in this area.
CUSAX: Combined Use of the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP)
http://datatracker.ietf.org/doc/draft-ivov-xmpp-cusax/