My experience was that you had to buy the phone card on that island. I bought a card on in the states and it did not work. The phones only used the calling card from that certain phone company and of course we don't have those here.
I had the same problem in the US Virgin Islands with a Canadian Calling Card. I had to buy a 5.00 card in St. Thomas to make calls back to Canada
May 2004 - MS Fascination Key West & Cozumel May 2005 - Carnival Glory Eastern Oct 2005 - MS Imagination 5 Day Western (Cancelled due to Hurricane Wilma) Oct 2005 - MS Fascination Nassau (Rebooked After Wilma) Apr 2006 - Carnival Victory Exotic Western May 2007 - Carnival Triumph Exotic Eastern Oct 2007 - Carnival Elation Baja Mexico July 2008 - NCL Norwegian Star Alaska Oct 2008 - Carnival Imagination Key West & Cozumel (on board 3 years late)