Not exactly, my dad phoned me from Holland via Skype today. The quality wasn't perfect but it saved him about 2/3 of the cost of the call to me in the UK and he reckons it will cut his bill for phoning my sister in Mexico very significantly.
I think it's probably worth a try, although in the UK you can get very cheap rates on international calls anyway, plus if the person you are wanting to talk to has broadband themselves you can do a voice and even video conference using Y Messenger or similar.