Well, after a long fight to try & phone someone with a touchscreen phone in the wet, I am going to take a slightly differnet tack:
1) buy a £12-15 handset with real buttons.
2) swap my sim card across when going out in the rib
3) Put it in an oldschool watertight bag.
4) live live without the internet for a bit
Online maps? I got a plotter a backup Garmin, and some laminated charts in the seat from the days before I had the garmin. I can live with my phone being just a phone for a day...