You can call anybody on your Skype, Google Talk contact list for free, they can call you as well. Isn’t it a life saver?
I’ve tried Fring from both the ends, voice quality is fairly good, but the voice gets choppy inside buildings or basements (I guess, that’s quite natural). To get Fring, go to their download page and fill-in some details, you’ll get a text containing the download link. As of now, Fring supports only Nokia handsets including N70, N72, N80, N80i, N90, 6630, 6680, 6681, 6682. Fring Fring!