You need to call Nextel/Sprint and have Jamaica turned on, (International rooming), and have one of the phones listed below. International rooming is turned off by default, blocking you from making a call.
Per the Nextel site you need one of these phones for it to work:
I have Nextel/Sprint service. In the last couple of visits, I've received a text message with 10 minutes of landing welcoming me to the Caribbean and telling me what the rates are for placing calls back to the U.S.
I know everything, and I'm always right (just ask my husband).