Excuse me for a moment while I wipe the last of the egg 0ff my face. It seems that Skype is not offering free phone calls to North American landlines, after all. The calls are free only if they are made within North America. Sorry for getting all your hopes up and thanks to EFL Geek for pointing this out.
Still, at 1.7 euro cents a minute it's still a cheap alternative to other phone services.