Don't know if it'd work 50 feet down, but stories of divers underwater, usually at their final stop or near the surface, having cell phones ring from their pockets are quite plentiful.Here's a question though: one time I forgot to take my cell-phone out and dove with it. Naturally it was fine, but would I have been able to receive a call underwater? Would have been strange hearing the muffled sound of my ring-tone going off at 50ft down. ;D
(Someday, I'll have to carry one down in an otter box to see where it loses signal.)