Sadly, in the last few years, private phone companies have taken over the port areas in most major ports and AT&T and other cards do not work in the port areas. You will have to either use a credit card or purchase a pre-paid card at the port to use the pay phones.
It's also one of the reasons that phone cards are not a great gift for cabin stewards or other crew members. Some of them have a number of "expired" cards in their quarters or can only use them once away from the port and often that time is very limited. Also, people don't give them the 800 access numbers for different countries thus making the card worthless.