Those having problems:
I've done quite a bit of testing/research on this. Hopefully I can help you all get your iPhones working!
First, the lightining cable shouldn't be the problem. I've tried it with three iPhones, and all worked fine. Plugging in the 30-pin adapter should not make a difference as the pins involved in the USB interface will transfer across the adapter without a change - so if it doesn't work without it, it should not make a difference with it.
With any of these USB audio interfaces the phone and the sound system have to have a "handshake" before they work. Most of the time, this isn't a problem - the first time you plug your phone in, the device will take care of this automatically. But sometimes, especially if the car has had other phone(s) plugged in, it needs to be forced to perform the handshake.
So, start by doing this:
- Start with your phone unplugged. Turn it off (hold power button until it turns off).
- When the phone is off, plug it in to the car.
- Turn the car usb input on on the stereo unit
- Turn your phone on
If this doesn't do anything, keep the phone plugged into the car and hold down the home button and power button at the same time until you see the Apple logo pop up on the screen. This is how you restart your phone.
If after doing that you still aren't up and running, the next step is to check on specific errors. If you are still getting an error, could you post what the error is?