Calling cards for Jamaican friends. What is the best kind to buy in the U.S. to bring for gifts and “tips”?

Calling Cards
dENISE D asked:

I’d like to make sure they are easy to use on the island. If I cannot buy them in U.S. where in Jamaica should I look. Does the airport sell them? Do I need to know what phone co. they use? Thanks for any help.