Mumble
From OpenSimulator
Initial Wiki page on development of an alternative voice module for OpenSim
Mumble - Murmur - Whisper
Initial information is available via these links:
The Whisper solution from vComm was the idea of Volker Gaessler, founder of vComm, and works by replacing the SLVoice.exe executable with a Mumble client that looks exactly the same to the viewer process.
You will use the unchanged Mumble server (called Murmur) and a region module called MurmurVoice. Communication is over ICE. The module including instructions will be available when the source code is published.
See also Freeswitch_Module