Free International Phone Calls?

I just read in David Pogue's column in the NY Times about Futurephone. If you have a unlimited long distance calling plan on your phone service now, you call their Iowa phone number, 712-858-8883, then dial 011, the country code + the number you want and you can have completely free international long distance phone conversations. Over 50 countries are included in the service. No registration. No fee. No nothing.

The only limitation is that it doesn't include cell phones in foreign countries yet, so your recipient must be at a land-based number.