Amazing Case for iPhone is on this iDive H20 Audio Deep Waterproof Case for iPhone 3G. It will allow you to watch your iPhone movie in the deep water, because it is completely waterproof down to 300ft or 90m underwater.
iDive Waterproof Case also provided an Over ear speakers so you can attach it to the mask strap or tucked under a dive hood. From its looking, it might be a bit bulky and heavy in hand. But when you stay in the water, the weight will not as heavy as it looks. iDive also has a built-in amplifier, so practically you can hear a good sound quality even if you are inside the deep dive.
[Price:$349.99 at Amazon]