The white iPhone 4 has been as elusive as that famous white whale, but there are rumors that it may be available soon. But if you can't wait, or more likely, you've already given up on the white one and bought a black iPhone 4, you have some options.
I just got back from a cruise and I used a $25 Trident Cyclops case to protect my iPhone from sand and water. While Trident doesn't claim that the case is waterproof, it's dust (and probably splash) resistant. Indeed my phone survived a week in Mexico at exotic locations like Puerto Vallarta, Cabo San Lucas, and the kids pool on the Disney Wonder!