Think there is a new phone on the market that is waterproof and can do underwater pics and video too
I use a secondhand iphone 3gs on a giffgaff pay as you go sim, very very cheep, an if I break it I'll just get another.... again
My Blackberry can't handle any water but the 2 iphones I've had are much better.
The cheep rip seal bags work very well, but if you get a nice case then make sure it has a thick neck strap as the string type cuts in after all day out on the water.