There are many different FREE programs that let you do this. Perhaps the most popular and easiest to use is Skype. SKYPE is the major leader of computer to computer telephony in Europe and if you know someone computer savvy there, they may already know all about this.
The software is free and is run very much like Yahoo Chat, MSN, or many other instant messenger services in that both of you have to be on the Internet at the same time, and running THIS software.
Clicking on the word "skype" above takes you to their website where you can quickly and easily download their software.
Here are some screen captures of what you'll see.
