GOgroove SMARTmini BT ADVANCED Wireless In-Car Bluetooth FM Transmitter with Charging, Music Control and Hands-Free Calling for ANDROID, iPhone, Blackberry and Windows Smartphones
This worked great with my iPhone 4S via bluetooth and using the FM Transmitter.  All controls worked as advertised once I removed the unused audio cable.  I thought I could leave the cable plugged in, but when it's plugged in even if you're not using it none of the bluetooth controls work.  The only complaint I have is the volume on phone calls is lower than music.  I don't make/receive calls that often so it doesn't bother me.  A nice feature would be the ability to pair more than one bluetooth device and 