This subject has appeared various times before.
Since the cards referenced by Jim Hinsch have add-ons, it is hard to determine the true cost per minute - what about the order handling fee + the value deterioration rate (both the weekly rent and the drop dead date) + the pay phone surcharge (in my experience, about 40% more than they advertise).
Do they have a contact 800 number for complaints? Also in my experience, they seem to have an accelerated rate schedule as time runs out on the card. Since they don't do a good job of telling how much time/money is left, it's hard to audit. It seems that many times I have been told at the start of a call that I had 10 minutes or so to talk, only to be told 3 or 4 minutes into the call that I would be disconnected in 1 more minute.
Therefore, I prefer internet computer-to-telephone connections now. Dialpad, for example, charges an almost honest $.13 per minute from the U.S. or Canada to the Dominican Republic. (I don't know whether the calls from Canada are in U.S. or Canadian cents). There is an expiration date, but it gets rolled over if the account is recharged before then.
Amount remaining is displayed. The duration of the conversation is also displayed, such that the user can audit the charges.
Finally, one doesn't have to enter 40 odd numbers to place one, perhaps busy, call. Just a few mouse clicks will do, at least after programming the number into the list.
If I don't have access to the internet and must use a call card, I settle for Sam's club's version of the AT&T call card - about $.16 per minute with no add-ons or value deterioration.