This is the Proscope Micro Mobile, a tricked out underwater camera bag designed specifically for an iPhone.  Not only does it fit your iOS device, but it has a build in ‘macro’ lens and light to illuminate small critters and corals.  With the advent of super megapixel sensors in common smart phones (8MP-12MP!) you can actually do a very professional job with these pics and also capture video as you chase your wrasse around the tank.  You can pickup the Proscope from Bodelin Technologies.