I do the same with a free 415 (San Francisco) phone from sipgate.com (redirected from google voice to have free sms &#38; calls) and an asterisk box. I use a sip client from my iphone only when I am on wifi (which is fairly easy in this city). I use voipcheap to call internationally (10 Euros last me for close to six months, which is the only cost of the system.