The thing that I would love is if I could control my Incredible with the buttons on the head unit, at least to have the ability to skip tracks forward/back by pushing the radio buttons. As far as I can tell, this should be possible given the hardware. There are kits that use the CD changer port on the radio to control an iPod, so we know we can get the track forward/back buttons sent out. And we know the Incredible will take headset commands like play/pause, answer, voice dial, and track forward through the headphone jack (I know this partly because these are the things my Incredible does when it is going crazy from the TRS input).
So is there no adapter that will connect to my car radio CD changer port and send the radio button pushes out as TRRS headset commands? I am really surprised this doesn't exist, but have searched around the web to no avail. Considering trying to build something but I don't have experience with an electronics project of this scale.
Alternatively, there is probably going to be an audio in/out + remote control for the Incredible usb adapter at some point, like the one for the Droid Eris. I assume this will be available since we know the Incredible is wired for audio through the USB port (I know this from the videos online where the Incredible does video out with audio through the USB). So this would appear to be another option for running the car radio commands into the phone.