via whistlephone.com
I was running low on my cell phone minutes and decided to get Whistle. They have an app for the iPhone, iPad as well as your PC. Technically, you should be able to call any phone in the US for FREE using WiFi. I tried it out already and the call quality is just like regular cell phone. Finally, a true Vo-IP that is completely free. If you were able to successfully use this, please leave comments!!