The last warterproof phone (meaning guaranteed if it got damaged by water) was the nextel i700.
Put your phone into a ziplock baggie and zip it shut. Insert that, zip end first, into another baggie. Zip that one shut. (Test the bags without a phone first - some brands leak.) Now you can toss any phone into the water. (Hose the baggie off first, then let it dry, before opening anything.)
If you fasten (no holes, please) a large key float to the baggies, even if you drop your phone over the side of a boat in a deep lake, all you have to do is reach out with a net and get it back - it won't sink. (You should see the jaws drop when you nonchalantly ask "Does anyone have a net, I dropped my phone in the water", then bring it back and finish the call you were on. You'll be able to sell the bags for $5 a pair.)