Skype.com - Best Free Internet TelephonySkype lets you call and speak to any other Skype user in the world from your computer for free. All you need is a microphone and a speaker.
You need Windows 2000, XP or Vista to run Skype.
You can also use Skype to make calls to ordinary telephone numbers all over the world at a low cost. You can find more info on discount international phone calls using Skype at http://www.skype.com/intl/en/allfeatures/callphones/.