Friends cruising used T-Mobile throughout the Caribbeean. Speed varies and T-Mobile says 128Kbps service, 256Kbps service available. Google Fi is another option I have friends mention, with faster than T-Mobile unlimited data in some placed at $10 per Gbps.

Someone asked about the ATT international roaming. For $120 you can get 800Mb for 30 days. I used that in June for our STM/Anguilla/BVI trip and it worked fine. In two weeks I ended up using up most of the allotment.

Cheers, RickG