The case provides a TOTAL waterproof solution for your iPhone 4 even with the 'Incipio Feather Case' which i had attached.
The whole screen is totally responsive through the rubbery screen (out of the water) but you have no access to the power button or volume controls. You can always set your timer to switch the phone off and adjust the volume through the settings.
I tested it first in a bowl of water then full submersion in the sea AND a swimming pool. If sealed properly not one drop of water enters the case and makes it possible to video what ever you want totally under the water. Still pictures are possible too but only if you use a timer as the touch the screen is not responsive under the water. A free photo app (I used 'Gorillacam') solves this problem by setting the camera to take photos after a number of seconds and even a burst of 3 shots.
The only weird thing is that the half of front facia is slightly opaque, i have no idea why but it does reduce the visibility although you do get used to it.
Follow the given instructions and should have no problems.
9/10 Stars!!! oh.. ok. 5/5