I'd personally recommend Ventrillo, been using that for a long time and it works great, lots of features (rooms, etc) and very customizable to sound great and be bandwidth-friendly. go here:
http://www.ventrilo.com/download.php
if you don't have a static/mostly static IP then go get this:
http://www.no-ip.com/
I know it all sounds like a lot of work, but it's all free and worth it ;) not to mention no-ip is good for many other applications as well
Edit: this is through a mic, not a phone - though even my crappy $4 mic has served me well ^^
Edited, Sun Sep 12 18:32:46 2004 by Armaddon