Prior to the iPhone 4 my 3GS worked pretty well in the Magellan Car Kit. I really only had one major issue and that was the phone overheating. I'm not sure if it was from the sunshine coming through the windshield or the car kit itself heating up the iPhone beyond it's tolerance. On several occasions I'd have to remove my phone, power it off and hold it in front of the A/C vent to cool it off. I eventually began running the A/C through the defrost to try and keep the phone cool. But because it didn't blow directly on the phone my results were mixed. It seems to me using either the Tom Tom or Magellan Car Kits with the iPhone is dangerous in the sense of heating up your phone too much. I think standalone GPS devices are engineered and manufactured with materials to handle being in the sun. Whereas the iPhone was never meant to be exposed to such hot temperatures. I've tried two solutions to keep the direct sunlight off the phone. One was to create a sun-visor attached to the car kit. But after a few days I wasn't satisfied with that solution. So currently I'm using a makeshift deflector (see attached image) to force the air from the Defroster directly onto the car kit and phone. This actually seems to work pretty good. When the A/C is on the phone can be on and exposed to the sunlight but only be slightly warm. I'm still testing it out, but so far so good.