The idea is simple: Griffin's Hands-Free Mic + AUX Cable ($30) turns your car into a speakerphone for the iPhone, iPhone 3G, or iPhone 3GS: you plug the cable into the iPhone's headphone port, the combination microphone and plug into your car's auxiliary input, and talk away -- the iPhone's call and music audio plays through the car speakers, while your voice gets picked up by the chromed microphone. Additionally, an in-line remote control button…
