H323 (which is a umbrella standard encompassing lots of protocols) is used by most VoIP applications, commonly used among these in applications like Netmeeting is G.729 and the voice quality is really good, at about 13k each way you dont need much more than a 128K connection to get good results. However, with a little tweaking you can get G.711 running on Netmeeting (its CITTT in the Audio options) and that is uncompressed voice at 64k - as good as a traditional telephone service - give or take a bit of delay for transmission. You can get this running no problem if you have a 512k connection.
With P2P the quality will be determined by the protocol that the application decides to use, and the chances are that it will either be the same as whats available already or potentially worse depending if any nodes on the net have been optimised to recognise H323 traffic or not. Which to be honest - they probably have not - but there a hell of a lot more chance of it than any P2P app has.
In reality this is just a lot of hooha about nothing - we already have these capabilities for free.