TMobile will work but it works on their international plan and of course you get charged international rates. TMobile is not as expensive as some but every international phone plan is expensive in Belize. I am on the island from time to time from a few days to a few weeks. I decided that the best thing was to buy a phone locally and get a local phone number and that is what I do even though my iPhone is unlocked and I could just put the local (in my case BTL) sim card. I don't do that though and just turn off my iPhone (TMobile) while I am there and change my voice mail to tell people to call me on my local number. You should be aware though that BTL will deactivate your account and you will lose any prepaid time if you don't use the phone at least once every couple of months.

Captain One Iron