I don't know if Barbados is completely independent from the US with the cellular network. If yes then this is what will be applied.
Little reminder! It is very important to add the add-on before arrival and also add these: International voice roaming 0$ and international data roaming 0$ (if you want to use your mobile data)! Everything can be done easily via your Account Self-Service http://koo.do/1dwzwBg.