Um depends where you want to call. Seriously, all those calling cards from the US are a joke. It's just like people who go to T-Mobile store and spend $200 on a phone. I can get you a K750i retail boxed and in mint condition for free.
We cheap asians know the best ones. 3 cents a minute to Hong Kong and Taiwan? ROFL!!!! Yes. Buy the Chinese ones. You just gotta talk to some Asian ppl about it and ask them which ones are good. If you buy the wrong ones, you will run into a lot of busy phone lines. Otherwise, the one I use now is superb. Yea and my friend brags to me about his stupid Verizon service that allows him to call India for like 5x the price I can call. Hell it's more expensive than SBC international rates.