Skype has a promotion going on right now. If you download and install their software on your computer, you can make free phone calls to any where in the US or Canada.
I use Skype, and I have been pretty happy with it. I don't own a regular phone, and I use Skype to talk to my friends in different places. All I use is my computer, my broadband connection, and a headset (speaker and mike).
Their International rates are pretty good to most countries, see: SkypeOut international rates. SkypeOut is their phone service from your computer to any phone. Calling from computer with Skype to computer is always free.