Can't all smartphones/tablets do this?

This is pretty old news, I've been using Google Voice and GrooveIP for well over a year now. I would imagine this is pretty easy to do with iPhone as well, right?

If you still have an old Android phone around that doesn't have voice or data service, this will help that become a usable Wifi VOIP phone as well. I keep my old HTC Incredible handy and it serves as another house handset since I forward my Ooma home number to Google Voice.