Yeah, I looked at quite a few protocols. The G series, H series, and SIP. I'm not interested in protocols since I have my own and I don't need to adopt a standard at this time. I'm interested in the compression or filtering techniques that can help reduce my 8000Hz sample down to a 4000Hz or smaller sample which can later be reconstructed and played. Even 4KB/sec is a bit demanding, but I could easily offer an option to go as low as 1KB/sec for those unable to handle any more.
Currently most of these protocols use a linear prediction scheme, but that's the core cause of all the scratchy, garbled up voice problems you hear in games like Halflife or regular VoIP programs. MP3 Pro deals with such a situation perfectly. It uses a technique called Spectral Band Replication to restore high frequency components back into the wav stream. It even supports quality as low as 18kbps, which is more than ideal for lower end connections. But those damn licensing issues just tick me off. If there's a similar technique that I can use, that would be great.