Whistle Phone App – use iPad as phone

The whistle app allows you to make free calls in USA from anywhere in the world where Wi-Fi or 3G signal is available. 

whistle-phone-ipad

It features free whistle to whistle calls and ability do 3 way conferencing. It works well, but I would be even better if it was possible to receive calls in the background. The app is absolutely free so I cannot complain much. [link]