A new IETF draft was submitted today which defines a SIP binding to iTIP. per the draft "This memo defines two new event packages for calendaring events; the first allows sharing of calendar events and the second of scheduling events related to calendaring. Using these two event packages, we in effect define an iTIP mapping to SIP." Until posted to the IETF it can be found at: http://people.nokia.net/~aki/drafts/draft-niemi-sipping-cal-events-00.txt