How concerned are you with listening to the radio? If you just want to play music from you phone and not have a radio you could get a small amp and use an 3.5 mm to rca patch cord to plug it directly to the phone. Use the amp to power you speakers and the phone for music. You could even put a volume control between the phone and the amp if you don't want to use your phones volume control.

If you want to be real slick, get an amp with a remote volume control and hook it up to a Bluetooth receiver and stream you music wireless. I've thought about doing this and removing, gutting, the radio's volume knob and replacing it with one to control an amp.