At work somebody pointed me to Skype. I had seen it before, and experimented a bit with it in the past but never really used it.
However, being in Puerto Rico and all, it is very easy to make calls to the Netherlands. Good phone cards are hard to find here, and it's difficult to coordinate for someone to call me (sorry paps & mams!).
I just installed in on my laptop and spoke for a little while with a colleague in Virginia. That worked pretty nice, so I'll keep it installed and experiment a bit more with it over the next days.
So, for the technically inclined: my Skype name is guusbosman.