The white WPI10 Waterproof Case for iPhone from DiCaPac provides you with a way to stay in touch with everyone while in the water. The case is submersible up to 33.2' (10 m) and comes with a handy neck strap that will permit you to splash around. Closure is easily achieved via a zip, press and seal maneuver. The PVC covering is designed so you can talk and hear right through the case. Full access to the touch screen is maintained. There is even a soft lens cover that allows you to shoot images. The anti-fog coating will help you get some great shots during your swim.
Another value to the case is that even if you don't go in the water, it delivers protection from sand, wind and other contaminants. An added benefit is that if you accidentally drop it in the water, it will float, so you'll always know where it is.