It is WhistlePhone that makes it possible to make unlimited free calls to USA from anywhere.

It is available for computer, MAC OS X, iPhone, iPod Touch and iPad.

It is free because when you make a phone call in USA from anywhere the call will have an audio ad in the beginning of the call. If you use whistlephone on iPad, iPhone or iPod touch you will see a small display ad. These ads are notifier that you can call to US for free from anywhere.

This service is free with audio ad, and you call free in US (US Phone Numbers) only if you call somewhere other you will have to get WhistlePhone balance.

You can make free call using Internet connection with or without Wi-Fi and 3G.

It is useful if you have customers, friends and relatives in United States.