Voice Over IP for Linux Games?

fathom asks: "A few friends and I are attempting to move all of our gaming from the Windows platform to whatever distro of Linux we like. For the most part we've all had great success: just about everything we play is fine under Linux. However, there is one major drawback: we don't know of any software programs for Linux to do Voice Over IP like BattleCom, RogerWilco, and the GameVoice. Are there any programs out there like this for Linux?" Why limit to Linux? What Voice Over IP software can be used for any Unix that's flexible enough to work for other applications as well as games? We did a similar question about a year ago; has anything changed since then?