For those of you who want to use the existing Radio 9 or Radio 10 with an iPhone (or any other MP3 player), here are the very simple instructions. Buy adapter cord lets you plug your headphone jack into the minijack connector found inside the glove compartment. Also obtain a car power adapter for your iPhone and plug them into the car. The AUX jack in the smart is inside the glove compartment. Start playing your tunes, and switch the radio to AUX. There you can control the volume, treble and bass. Nothing else can be controlled from the radio.
If you want to make calls, get a Bluetooth headset, or trade your factory radio for one with Bluetooth capability. If you want to control your iPod or iPhone music from the radio headpiece, check out Crutchfield.com for a long list of radios that fit the double-din slot of the smart.