What is Skype??

Skype is a proprietary peer-to-peer Voice over IP (VoIP) network founded by the entrepreneurs Niklas Zennström and Janus Friis, also founders of the file sharing application Kazaa. It competes against existing open VoIP protocols such as SIP, IAX, and H.323. The Skype Group, acquired by eBay in October 2005, is headquartered in Luxembourg, with offices in London, Tallinn and Prague[1].

Skype has experienced rapid growth in both popular usage and software development since launch, both of its free and its paid services. The Skype communications system is notable for its broad range of features, including free voice and video conferencing, and its ability to use peer to peer (decentralized) technology to overcome common firewall and NAT problems.

VOIP, like MSN.

browse the website below to get your answer.
http://www.skype.com/intl/zh-Hant/

Skype is a little program for making free calls over the internet to anyone else who also has Skype.
All calls from Skype to landlines and mobiles within the US and Canada are also free till the end of the year.
It’s free and easy to download and use, and works with most computers.