Very good, cost-effective solution

I had previously. For my iPhone (on Audio 20 CD, MB A-class, Bj.2005) another FM transmitter solution with gooseneck who was very annoyed me conclude (Had 2 years ago cost about 70 EURO). Constantly Contact problems at the interface. The iPhone is so it stuck when you get in the car and wants to listen to music. The design is just as time increasingly shaky and contact problems are increasing.

The FM transmitter I use only for the music transfer from iPhone by BT and FM one on the car stereo. And he can be very good and sound very impressive. However strong FM station press for longer trips sometimes pure, so off-and-on a light dross on crosstalk. But is rarely happened previously; you can then, if necessary, to select another frequency (is the drive but a bit fiddly ;-).
Handsfree via iPhone I do fundamentally with an additional BT headset, because thus the voice quality is significantly better (because a headset is just closer to the ear and mouth ;-). Basically, yes many smartphones support parallel BT sessions. Come in a call, the FM transmitter automatically turns off the music transfer.

So, I recommend this solution. Good sound and good workmanship at low cost.