You can get your Verizon phone to work in Belize
This of course is "working" in the sense that it will be able to roam onto the BTL network. Coverage will be BTL coverage, and of course as has been stated you can expect costs to be enormous, but fine for just emergency usage. If you want to chat on the phone your best bet would be to get a prepaid BTL Digicell SIM card ahead of time. Maybe BTL can provide that via their website, or perhaps someone here can help (buy it and mail it to you). So long as it has on-board credit of at least US$25 that credit will be good for three months, so bear that period in mind when you get it.