I don't know if any of you watch Tech TV (it's for computer geeks), but there's a program they advertised on the Screen Savers that allows you to call anyone else in the world thru your computer, for free. All you need is to have either Windows 2000 or Windows XP, a microphone and speakers. You download the program, and then the person you're calling needs to have it on theirs as well (meaning, they also need Windows 2000 or XP). Again, it's free to download, and allows you to make free calls anywhere.

This kind of explains about it:
The Screen Savers

and this is where you can download the program:
Skype