I'm using the HTC Touch Pro trying to do the same kind of setup. It seems that in order to get my phone into headset mode, I have to connect 'Mic -' and 'LG,RG' together. The 'S' line is used for the switch. When I connect the 'S' line to ground without pulling 'Mic -' to ground, my phone goes into video output mode. I couldn't find any documentation on this stuff and I thought that this info may help anyone else trying this kind of project.
Good work on the car connection! Looks like a kludge, but that's just the way I like it
