iCall, iPhone, it's VoIP

Even the iPhone will have its special VoIP application, the software it's still in development and it will be released for sale or for free in the App Store, dedicated exclusively to the iPhone, merging into it, will allow VoIP calls using the Wi-Fi connection integrated into the phone so make free or paid VoIP calls, depending on the destination Country.
iCall is available also like a Windows 2000/XP/Vista software (see the download page) and, at the moment, it allow free VoIP calls over US and Canada, with a 5 minutes time limit per call for the Basic version of the software.

Link: www.icall.com