Tom!!! I still owe you that book. 🙂 Very interesting thread you started.
I am pretty protocol agnostic and I believe all will have their place. I believe that MGCP or megaco or some variant thereof will prevail in the carrier community.
SIP will have its place and soon…windows messenger in XP is SIP based which makes it immediately pervasive. SIP definitely lends itself to mobility and anything that relies on intelligent endpoints.
H.323 V3 IMHO did not bring about enough changes to “simplify” the protocol…it still uses ASN.1 notation, but it did bring about annex E and annex G. IMO v4 will have more impact than v3.
At the end of the day, the battle between SIP and H.323 has become more marketing hype and political, but at the end of the day I think SIP will become prevalent. It will still take another 2 years or so to get more traction. Lets keep in mind that a vast majority of VoIP networks out there today rely on H.323. That being said, everyone seems to be relying on these protocol translators to help the adoption of various protocols. There are a ton of issues in this space that I dont even want to touch right now.
ITU standards are just too slow to bring about change. IETF is just plain faster. SIP is already on bis06.