Say you want to send a billion messages per day without paying a cent out of your pocket. I don't think that's physically possible, but it's theoretically possible using WhatsApp.
This app doesn't use SMS, it sends instant messages over the Internet.
With WhatsApp, you'll be able to send instant messages, pictures, videos and voice notes or group chat without using SMS. It uses your own phone number and integrates with your contact list so you don't need a user name or PIN.
Whether you or your contacts have iPhones, Android phones, Windows phones, Nokia or Symbian, you'll be able to use WhatsApp. That's because it's a true cross-platform, Internet-based service.