There are several eco friendly cases available for the iPhone 4, such as this one from Agent 18.
The Eco Shield for iPhone 4 looks like alot of the mobile cell phone cases out there except that it’s made from recycled soda bottles.
The Agent18 EcoShield+ ifor the iPhone 4 designed to be both user friendly and eco friendly. The patent-pending technology includes a built-in stand, speaker amplification design, and a sliding headphone jack door for added protection against environmental damage. A rubber overmold adds additional grip, button protection, and shock-absorption and the bottom half removes for easy docking. The closed stand provides full protection for the 30-pin connector. The stand rotates open for Face Time usage and watching movies. The eco-friendly part comes from the fact that the cases use at least one recycled plastic bottle in every case.