Don't know about Cayo district, but BTL has excellent coverage in the cayes off of Placencia.
BTL has coverage for most of the areas behind the reef. If you dont see signal then stand on deck
as high as possible and face the back of the phone
towards the nearest cell tower...these towers are usually near the closest town...at night you can often see their red flashing light for a better fix. Not likely to get coverage down in the Sapodillas. *
Basic cell phones do better than fancy ones. My theory is that the basic phones have more room for the internal antenna
than the fancy ones w all the other stuff crammed inside. My old Nokia dumb phone
out performs smart phones every time...I've joked with guests w fancy phones, which could not get signal, about renting
it to them.