The iPhone 4S is not yet listed as a compatible device with the Mki range, we are currently working on problems observed during testing to find a resolution.
If you don't get sound but the music is shown as playing on the MKi9200 screen unplug the dock from the iPhone 4S and reconnect this. You should now find you get sound.
If you still don't get sound please check the Mute on streaming setting is ticked on your MKi9200 SETTINGS>AUDIO>MUTE ON STREAMING
Not exactly the safest thing to do whilst driving this is also a bug with the iphone with IOS 5 and 5.01
This could turn legal very quickly if someone has an accident due to the defective nature off substandard firmware.
Also are you going to delete this post aswell which your very good at doing