Apple is always ready to test heavily marked-up case designs, and iPhone 4 Bumper ($29) is its most minimalist case yet. Available in six colors -- one per $29 package -- a Bumper is a thin glossy hard plastic band that wraps around the iPhone 4 stainless steel center frame, with rubber front and back bands that hold the iPhone 4 inside. There's no protection for the front or rear glass of the iPhone, save for the extra millimeters of depth added…
