Cell phone coverage in NW Florida is a whole story in itself. AllTel is still by far the best coverage, even out into the gulf. They were the only cell phone system serving the area for a long time, even to the point of locking out the other providers. Then AllTel over-extended and went bankrupt. They closed most of their offices and then suddenly reorganised with funding from some of the other providers, who (poof!) got instant acess to the area.
The best bet, especially if you are living there, is to get an AllTel 'pay as you go' phone (that's what I use down there now) from a wal-mart or drug store in the area you will mostly be in - you just buy a set number of minutes on a phone card and put them into the phone. It's cheap, so if it falls overboard it dosen't matter. There is no contract, no phone insurance and its a easy no frills solution.
If you are just visiting, keep your real phone for back home and reload the 'Florida Phone' minutes for the next trip. The AllTel phone also works in Gatlinburg and other areas where the other phones don't, but may use 'double minutes' sometimes in those areas.