Can I use any AT&T calling card in countries outside the USA?

I need to find an international calling card and I have a friend who uses a standard AT%26amp;T card he buys at Wal Mart in other countries to make calls. But when I read the back of one of those cards it says "may not work internationally." Is that just a disclaimer or do they sometimes not work overseas? What kind of calling card should I get that will work?

Can I use any AT%26amp;T calling card in countries outside the USA?
You can use the card in many countries outside the USA, but you may not get as many minutes as the card says...like if you buy a 500 minute card, you may only get 100 minutes if you use it outside the States...