I'd rather go for a candy-bar style with exposed (not sliding) keyboard for a survival type phone. You can put it in a zip-lock bag and make it waterproof but usable instantly as the need arises. Also they might have dozens of dedicated protective cases or skins available on the market, which you can wear on the phone permanently. No doubt the candy bar is more reliable just by design (no moving parts to break), and the battery is often of a larger capacity in them. Regarding the carriers, Verizon - is still the best in the coverage department (on the West side at least).

Just my 2c.