Are you looking for a setup like this?:
iPhone>Bluetooth audio signal>Bluetooth receiver>3.5mm connector>Car Stereo Aux IN
If so, so am I.
I'm going to order this one:
http://www.amazon.com/HomeSpot-NFC-enabled-Bluetooth-Audio-Receiver/dp/B00G57CWZ8
My reason for this is that it gets power from USB and doesn't have a battery. It powers up with the car and pairs automatically with your phone (if it's not powered via an "always ON" type cigarette lighter/USB plug).
For me, the devices with a rechargeable battery are problematic as most, if not all, need a button push to initiate pairing and ours will be hidden in the center console.
I won't have it installed until next week.