According to various sources, Skype is using codecs from Global IP Sound.
GSM - fixed bit rate, not loss tolerant, narrow band (8khz sampling rate).
iSAC - variable bit rate, loss tolerant, narrow and wideband (8 to 16khz). Varies based on Bandwidth, packet loss, delay
iLBC - variable bit rate, loss tolerant, narrow
g711U/A - fixed bit rate
EG711 (enhanced g711) - fixed bit rate, loss tolerant, narrowband
iPCM - fixed bit rate, loss tolerant, wide band.
According to Gizmo Project support site, audio is powered by Global IP Sound.
According to: http://www.google.com/talk/developer.html Today, Google Talk supports the following standard voice codecs: PCMA, PCMU, G723, iLBC. We are also evaluating the Speex codec. We also support codecs from Global IP Sound: ISAC, IPCMWB, EG711U, EG711A
For more Global IP Sound customers go to their website.