According to http://pinouts.ru/CellularPhones-A-N/iPhone_connector_pinout.shtml two of the pins in Apple's 30 pin connector are dedicated to line in. I have spent days looking for a cable with line in capabilities (because I want to record stereo line in, the headphone jack is mono and is not line level) but they are nowhere to be found. I can only find http://line6.com/sonicport-audio-interface/sonicport/ and similar that are way to bulky and unnecessary expensive for my purpose.
Do I suck at Google? Does it exist simple 30-pin cables with support for line in? If not, why? The reason I ask the last two questions is that if such a cable doesn't exist my plan is to find someone in a music shop or similar and ask them if they cold make/solder such a cable for me.