Skype is a voice over Internet protocol (VoIP) application that lets users make free phone calls between Skype-equipped computers and inexpensive calls between Skype computers and landline or cell phones. Skype functions on a P2P model rather than as a centralized application, and it offers features such as voicemail, call forwarding, conference calling, and video chat. In most circumstances, Skype provides access to voice and video communication for a fraction of what other options cost. It allows more frequent contact between colleagues, collaborators, and friends and permits connections with those not likely to be in touch through conventional phone systems.

http://www.skype.com/intl/en/download/skype/windows/

How to install, test and use Skype:

Getting Started with Skype (PPT)

Using Skype in your classroom
http://www.teachingdegree.org/2009/06/30/50-awesome-ways-to-use-skype-in-the-classroom/
http://www.dummies.com/how-to/content/using-skype-at-school.html


7 Things You Need To Know About Skype
http://www.educause.edu/ELI/7ThingsYouShouldKnowAboutSkype/162373