17-02-2017 14:23 - edited 17-02-2017 14:24
You need to look here if you are texting a Jamaican number, note it may be different for pay monthly and PAYG so pick the correct type. http://www.o2.co.uk/international/internationalhub
However, if you are texting a UK mobile to someone on holiday in Jamaica it will be the same as if they were home in UK so free if you have a text allowance.
Lumia 950 Dual (O2 & Sfr) and Z3 Tablet (Three UK)