You can have that Cable to provide the audio to your Radio, and just get a simple 3$ iphone charger for car on ebay.. problem solved.. You can charge your phone and listen to music..
Or maybe some cable add some extra functionality like this one:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=200532817863&viewitem=&_trkparms=algo%3DLVI%26its%3DI%26otn%3D2&category=169337
Google (and ebay) is your friend..