Just a quick heads-up to let all our U.S. readers know that AT&T has launched its own "Voice over IP" app.
The AT&T Call International App will let you use your existing wireless service to make cheap international long distance calls with your iPhone. There’s no monthly recurring charge, prepaid balance or commitment term required.
Not being in the U.S. myself, I cannot access the app, so do not know how accessible it is.