Rui CarmoG.729 is one of the most efficient VoIP codecs available, but is sadly encumbered by patents and pretty much everyone is looking for a free, equally efficient alternative.
Resources:
- Open Source G.729 and G.723.1 - useful for development (requires Intel sample code, eye of newt and bat's wing - i.e., lots of assembly required...), but cannot be used in any sort of product without infringement.
- An unsupported .so for PPC Macs (requires registration)