For those of you who want the best quality out of your $30 smartphone plan, I made a 12-part video tutorial showing how to do it.
http://www.youtube.com/watch?v=u9DzN1Pu6-Q&list=PLE_de-PBwrTSUMm-Y48aiOOHt_YyT69t0
It's much better than GrooveIP, Vonage, Talkatone, Pbxes.org, and everything...