I would Never rely on a cellphone in an emergency, especially at sea. In my part of the world, the network coverage is not designed to cover offshore, the phone technology is really fragile in a wet environment [ just when you're probably going to need it ] and even in a dry bag, the phones are susceptible to condensation. Even a hint of moisture and the best phone goes down. <br>And I have recently read of GPS units supposedly waterproof, ie, the latest Garmins, have gone down after condensation and moisture intrusion.<br>I have a Silva Multinavigator GPS, supposedly designed from the get go for a harsh environment, but even so I am careful with it.<br>My cellphone is always in a drybag, with a careful watch maintained for humidity;<br>and my VHF marine radio is also in a drybag. Even marine VHF radios rated to JIS 7 standard should be considered not waterproof outside a drybag. They all tend to leak around the battery compartments.