BTL has a monopoly, so I don't think you can use anything but their cell phone service. You can bring your own phone but the only thing that counts is having the right band and mode. Make sure yours is TDMA 800 AMPS. There are some dual mode or multi-network phones being sold now that have that capability. Likely to find the right phone in the US if it is/was connected to AT&T or a really old network, as most of the newer digital networks are PCS 1900 and CDMA which won't work in Belize. The really old big chunky motorola flip phones also work. I brought an old cell phone (NOKIA 2160) down last month that a friend gave me that wasn't in use and BTL in Belize City activated it while I waited. Probably not the case now with higher demand.