i'm using a standard 3.5mm jack to phono lead to get the sound from phone to stereo. works fine with my iPod.
3.5mm jack on the lead is identical to the jack on my handsfree except the handsfree plug has the extra ring for the mic
i've checked the plug fit for length, girth and depth etc (should probably mention 10years audio visual experience at this point. house has so many cables my friends just call it the 'universal adaptor')
when i make a contact from signal to ground (by touching the left phono tip to the right phono earth) the headphone icon pops up on the screen and the audio stops coming out the speaker. i'm thinking the earth is too good on my stereo, completely isolated from signal. so unlike a pair of headphones where the current runs back down the earth, theres no return current on the earth line to tell the phone there's something plugged in. (this is fairly sensible - less moving parts means better longevity - but on the other hand means the headphone switching only works with headphones)
unless there's an app for this i'm just going to make up a cable with a 10k resistor between signal and earth on the left channel. not enough to cause a short or kill the signal, but enough to bleed a little through to earth and let my phone think there's something plugged in