If you are planning a real expedition on a sparsely populated coastline cell coverage is going to be poor no matter which carrier you use. The systems are not designed to support on water calling and service to outlying areas. If you are serious you probably need to look into satellite.
That being said I would suggest unplugging for a while. A few years ago I did a trip around New Zealand where my cell phone absolutely did not work, and internet access in small towns was terrible. It was quite a refreshing vacation- dare to unplug.
Rescue / Throw Bags
PFD's (Life Jackets)
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