We have introduced all kinds of protective cases for iPhone 4 and 4S. But if you want to add some modules for more functions, the following Aeris Rail+ iPhone 4 case may be able to draw your more attention.
The Aeris Rail+ is a practical modular protective case designed for both iPhone 4 and iPhone 4S. The iPhone 4S case is constructed of injection molded ballistics-grade polycarbonate, plus CNC machined medical-grade stainless steel button cover in order to protect the iPhone 4 or 4S from bumps and scratches. Most importantly, the unique rails on both sides of the iPhone 4 case allows you to mount various accessories for more useful functions, for instance, the Visor, a set of front and back covers, the Kickstand, an iPhone stand supporting both landscape and portrait viewing modes, the Ride, a handle bar attachment for mountain bikes and etc. Apart from that, the custom cutouts allow you access to all the buttons and functions of your iPhone 4 or 4S.
At present, the designer of Aeris Rail+ is raising fund on Kickstarter. Pledge $50 will let you own the modular iPhone 4 case with the Visor kit and kickstand. If you’re interested, jump to Kickstarter official site for more details.