Hi I have an iPhone 4 and would like to listen to music on the phone and use the GPS app while driving. None of the existing car solutions are satisfactory. FM transmitters all suck. There is nothing you can do about a) its sound quality (FM has limited bandwidth), b) the availability of "spare" or empty frequency slots changes as you travel through different cities/states on a long trip (or even just a short one, say from NYC to CT) while it's impossible to keep relocating the frequency and c) the problem of interference (even just listening to the radio stations has that problem). So my only option is the cassette adapters, most of which use 3.5mm jacks. I have two main issues with them: 1) I am not sure if shorting the iPhone mic is good. The headset that comes with an iPhone has four connectors on the plug: left ear, right ear, mic, ground. But cassette adapters only have three, without the mic. So essentially the iPhone's mic connector is shorted to ground. Theoretically that should not cause a problem: shorting it to ground simply means no input. But I am not the designer of iPhone and, without seeing the circuit diagram, I am not sure if they have other designs in that circuit that makes shorting the mic input not good for the device in the long run. 2) So if using a cassette player means shorting the mic input, I lose another function, which is making hands-free calls while driving. With an FM transmitter (when it works), the built-in mic on the iPhone still works. Not to mention that some apps have weird audio output settings that are often messed up between the speaker, the 3.5mm jack output and the dock-connector output. So....I guess, the question is, can I find a cassette adapter that does NOT use a 3.5mm headphone jack but the iPhone dock-connector as its input?? Also, I'd like one that can also charge the phone. (so basically that means two connectors coming out from the iPhone, one goes to cigarette lighter and the other goes to the cassette slot) Thanks!