I have found that the cards with not so low cost per minute and no connect (per call) charge work out better than the ultra low cost per minute with a connect charge. Typically a connect charge counts as 20 to 50 minutes.
Too many times I get a bad connection or an answering machine, and with connect charges, you do not get much talk time if you make lots of short calls.
All calling cards have a connect charge from pay phones (a second connect charge for cards that have a connect charge from all phones)
Sometimes at a hotel you may find a non-pay phone in the lobby that makes 800 (toll free) calls and after just one or two tries you can find out whether it results in no additional connect charge for you card.