There is a Digicel store right at the airport. Bring your Samsung down and they will put a chip in it. If it's not suitable they have phones for sale. The website only shows some expensive Samsung but the last time I was in they had some inexpensive stuff on display.

When you walk out of the airport, instead of turning right and heading to The Groovy Grouper for an icy cold Red Stripe, turn left and the Digcel office right there.