Upgrade your head unit. Most come with USB and Bluetooth these days and support iphone either by way of USB or the traditional audio in socket.
This way you wont need a seperate hideous cradle showing the world that you may have somthing hidden under your seat / glovebox when your away from your car and the benefit of having everything intergrated including handsfree driving kit for cellular.
I've never met anyone who has stuck with FM given any other choice.
I put a Pioneer DEH-6450 in my new car. Best thing I ever did. A2DP streaming quality is great and works with no config other than pairing the iPhone. The hands-free mic works well too so I'm not having to pull over to answer the phone.
Haven't tried the USB for charging or audio but assume it will work for both.