+1 from me too.

You can survive without, but since a *most* people have one these days it seems foolish not to take such a useful tool with you. It can save your bacon in so many different ways.

If you don't want to be interrupted by it - turn it off.

I work in a water sports club and we ask people in certain boat types to take a phone in a dry-bag with them. That one in a million chance you need to be rescued is so much easier if you can phone for help (ie small boats that don't carry flares, VHF marine radio etc). Phones are cheap and reliable with dry-bags a bargain compared to the cost of the boats/kit that people buy (actually, we had a boat owner of a multi-million dollar Cat 1 offshore racing yacht complain about a new safety regulation requiring a new $1000 comms system! 20 people can die on your boat, a-hole, so just buy the new radio!)