from the people who brought you KaZaA = Niklas Zennström and Janus FriisSkype is the next phenomenon from the people who brought you KaZaA. Just like KaZaA, Skype uses P2P (peer-to-peer) technology to connect you to other users – not to share files this time, but to talk for free with your friends.
The technology is extremely advanced - but super simple to use... You’ll be making perfect quality free phone calls to your friends in no time! Just tell them to get Skype as well, if they don’t already have it.
More info here