Just an FYI...
San Pedro doesn't have 4G yet but Belize City and two other towns do. If you meet the following requirements:
1. Have a 4G capable phone (iPhone, Galaxy, Droid, etc)
2. Have a post paid account
3. Don't have 4G services on your plan (I would assume no one in SP has this yet unless you frequently visit the city since we don't have this in SP yet)
then you probably won't have data or phone service when you arrive in Belize City with you BTL SIM. Reason being is that your 4G capable phone is picking up the 4G but you don't have the service active on your account. For some reason it won't failover back to the 2G/3G active service. So you will have to call BTL and let them know that you have a 4G phone but you're from SP and don't have 4G services.
You may want to do this before you head to the city because once you get there you won't have phone service.
Just wanted to let you all know so you're not stuck in the city without a working phone.