Mobile Voip over XMPP

Mobile Voip is one of the hottest trends now on new generation phones. But what's the most efficient way to do it?
In a time that calling is not the absolute main feature, but another in a combination of: Calling, Presence and Contacts. Telecom companies choose to go for SIP/SIMPLE IMS based systems.
Well it turns out that we all know that it exists but we never saw it live in a mobile in front of us. I mean, at least in a way that the battery survived more that 4 hours or so.

Analyzing IMS specs you will notice that it is nothing but a lot of work around in order to let SIP do what he wasn't meant to do from the beginning. And another question that pops up is interoperability, as the specs are quite open to interpretation in several aspects.
Work-arounds like XCaps which is just a web service but behind a cool name and lack of a defined and more strict way for contact management are leading IMS implementations through a long off-road track. A race that they don't wanna quit as they spent billions of dollars acquiring already obsolete plataforms.

In the other hand XMPP have shown that Presence and Contact List are very simple doable things and that this can inter-operate successfully among different networks, devices and even protocols.
And now it has another advantage, which is the mobile Voip ability. Already deployed live for millions of users on Nimbuzz Network.
One of the coolest features of Jingle it is his almost natural way to deal with P2P negotiations, which leads to much better and reliable negotiation of media specially when compared to SIP.
XMPP Jingle demystified Voip showing the real simplicity behind it, removing all the obfuscated logics behind SIP tags, branchs, CSeqs and transactions. (Check MiniJingle as an example)

All this packed together can guarantee that whatever the market wants in next months and years, XMPP is way ahead when dealing with extensibility, simplicity and interoperability.
Which are the strongest tendencies for near future communication.