Right. That works great in an environment where the regulators require that every telco pay Neustar to maintain the LNP databases, and send all the updates promptly when a number is ported or disconnected.
The telcos pay Neustar $300 million a year to run the database. I'm sure they'd be delighted to run a similar database for IP networks at a similar price. Of course, that just handles the networks in the U.S.
One of the challenges in the VOIP world these days IS call routing based on destination DID. It's easy to ship calls out trunks; it's far more compelling to send them to the destination PBX directly over UDP/IP. Sadly, the best mechanism anyone has come up with is manual number publishing in an rDNS style database, and the results are less than stellar... Nathan