Weird. I always found skype a pretty cool thing for VOIP stuff, and an interesting setup for a company (give the software away, let people call eachother on the internet, charge for outgoing calls).
At voipbuster they do almost exactly the same thing, but with slightly more competing rates; EUR 1.30 (or something) for unlimited calls to landlines within the Netherlands, USA, and a couple of other countries. I know I sound like a commercial, but I actually think this is neat. And works on mac, if you go here. (I'm not affiliated in any way with either of these companies or products )