I'm trying to wire my 600 into my car, which is pre-wired for a dealer option phone. I've got everything working except muting the radio when a call comes in. The THB car kit can do this, so there must be a way to detect that the phone is in use. I've looked in the Developer's Guide, but couldn't find anything. Is a signal sent throught the audio or hotsync connector when the phone is in use? If so, does anyone have any details?