Remember when Buster found an iPhone at the bottom of a river while he was floating down it on an inner-tube? The previous owner had the right idea: he sealed it in a plastic bag to keep out the elements. But he forgot one thing: Even in a bag, the short, heavy, ugly iPhone 4 will sink like, well, like last year's crappy iPhone.
What he should have used was Coghlan's Dry Pouch.
Coghlan's makes all kinds of outdoorsy gear, and the pouches come in three sizes. The one you want, and the one our unfortunate iPhone loser should have bought, is the #1350 3×60-inch model. It seals in the iPhone, and the plastic lets the capacitive rays from your fingers pass through to the touch-screen on the other side (to be fair, most plastic bags do this).
It also seals watertight using a pair of locking tabs, and can be either slung around your neck or clipped to the top of your boat with a (supplied) carabiner.
Finally, it floats, and the yellow strip will help you (or Buster) find it in the water.
Like many outdoor products, you can't actually buy it from the manufacturers site, so you'll have to track it down using the store locator. I can't help but conclude that this is a test to see if you are worthy of owning outdoor adventure gear. vailable now — if you can find one.