Last week I attended the ITU GSR09 in Lebanon as you might have guessed from previous posts. I presented a discussion paper there on the future of VoIP interconnection. I didn't like my paper too much as I thought I could have written down the point a lot more poignantly and used less deductive reasoning, however other people disagree. The presentation is now embedded below and the paper is available here.
The main point I think you should take away is that interconnection isn't that hard. It is made difficult by lawyers and weird business models, but it is quite simple. The second point is that regulators should have a look at ENUM for a national number database, with number portability attached to it. They shouldn't care about Public ENUM that much as it mixes technology and policy in standard. The policy who can change and add what in the national number database is the domain of the national regulators and not of the IETF or the ITU. BTW it turns out Bahrain is going to build a national number portability solution based on ENUM.
(And yes, Logica makes number portability systems, but that wasn't the reason why I came to my conclusion)