I tried connecting the iPhone with the USB cable, after turning off Bluetooth. I like USB better than Bluetooth! At least as far as the interface. You have more control of which songs you listen to on the screen, while with Bluetooth, you can only play and pause. All control of track selection is done on the device, which means you have to be juggling it while driving. Much easier on the Leaf screen, at the cost of a cable flopping around.
Interestingly, you can turn BT back on, and toggle between USB and BT from the selection button on the console.
Thanks for asking your question, I learned something new.