We had a prepaid type card that came through with our tickets from Virgin. It is a Austrailian company, and basically you have an account number and a pin number. We charged the card up before we went with $20 (it has to be at least $10). Anyway, when you want to call home, you have to dial a 1-888 number. The message then asks you to enter your account number (which is on the card) then your pin. Then you just enter the phone number including all the codes, we are in the west midlands and we had to dial 0044 1384 XXXXXX. And you get all call at 50 cents a minute, we got 40 minutes for our $20 and it worked every time from all phones at the resort hotel (All Star Movies) or round the parks. You can top up some more if you wish and you still get the calls for 50 cents per minute. You also get a message box, so people at home can call a number (I forget which one, but it is on the card), enter your account number and leave you a message. You can check your messages whenever you want. My Mom called us and left a message to check if we had got there ok, and left one to say Happy Birthday to my wife.
I have to admit this card is an excellent service. We got all our calls home for $20 which is what £15?
Hope this helps
Steve