Skype is a free Instant Messaging App that also does really high quality free Voice over IP. Its easy to use, free, and the sound quality and lag are great even over wireless LAN and long distance. And did I say it was free?
It also does voice calling to real phones. That’s not quite free, but is cheap (probably cheaper than using a phone card if you’re making international calls.)
Go get it from www.skype.com. And if I know you, email me, we can exchange contact details, and start Skype’ing!