VoIP Codecs

Audio Codecs

ITU G.711 - High Quality, Low Compression/CPU Usage, Bandwidth: 64Kbps (90Kbps Real World) A.K.A uLaw/aLaw
GSM - Standard used by Cell Carriers, Bandwidth 13Kbps (40Kbps Real World)

Video Codecs

ITU H.323 - Intended for Video Confrencing

References

http://www.voip-info.org/wiki/view/Codecs