If you're looking for the thinnest and least obtrusive case available for the iPhone4, look no further. The Air Case is one of the thinnest acrylic hard cases available. Better protection than adhesive film covers but less bulk than standard plastic and silicone cases.
This case is clear so that you can preserve the natural beauty of the iPhone's design. If your into graphic skins but don't want to commit to a single design, the air case allows you to swap out your different stickers without having to peel away and discard them. Just get several of these inexpensive cases and apply your designs to the backs of these cases. Then you can swap out designs by popping off the cases.