SIP/SIMPLE is most likely to be the most popular.  MS selected it and it re-uses of existing infrastructure (proxies etc.).
 
There are standards and there are standards de facto. Where JABBER fits in?

From practical indistry point of view H.323 UNI solution (e.g. based GEF.3 well defined)  will enable H.323 Terminal developers to I/F with
SIMPLE based solution. 
 
From user point  of view (He decides the future of this):
Great multimedia and conferencing solutions (H.323) powered available IM/presence services.
 
-----Original Message-----
From: Tom-PT Taylor [mailto:taylor@NORTELNETWORKS.COM]
Sent: Wednesday, June 26, 2002 12:22 AM
To: ITU-SG16@echo.jf.INTEL.COM
Subject: Re: IM and T.140

"Instant messaging" in general is a really crowded field of endeavour.  The IETF had nine different protocol proposals in fromt of it.  After a heroic effort these reduced to three.  Now JABBER is attempting to expand the field again.  The IETF has defined a framework for presence and instant messaging to make it easier for all of them to interwork.  I suppose at some point we should look at how T.140 might be brought into line with this framework.
-----Original Message-----
From: Paul Long [mailto:plong@IPDIALOG.COM]
Sent: Friday, June 21, 2002 3:29 PM
To: ITU-SG16@echo.jf.INTEL.COM
Subject: IM and T.140

What's the difference between "instant messaging" in general and T.140? IOW, what can you do with one that you can't do with the other?
 
Paul Long
ipDialog, Inc.