Connecting Iphone to a portable stereo through usb !!

[alstonfered]

Hello Everyone,
Is it possible to connect my Iphone 3GS to portable stereo CD player with just the USB port?
I have tried by just plugging it in to the usb port and turning my Ipod on - but no music comes out of the speakers.
Although I can see it is playing the song on the Iphone.
Am I doing something wrong or is it just not possible?

 

[labman]

possible

but with out knowing anything about the radio model/make we can't tell you how! might read your car audio manual and see what it says.