OtterBox Impact Case for iPhone 3G, 3GS (Black) Impact Series™. The Impact Series line of cases by OtterBox reaches those looking for less extreme, more slim-fit protection. By incorporating the successful Silicone design used in the Defender Series™ line, the Impact Series provides effective protection against bump and shock. Apple® iPhone 3G Impact Series. The OtterBox for iPhone 3G Impact Series provides complete user interaction and access to all the iPhone's functions. The inner corners of the case dissipate impact away from the iPhone 3G for effective protection against bump and shock.