Originally Posted by techgeekwill
some of them would interface through the AUX jack.
I'm not sure if outputting the phone audio to the AUX input of a head unit would be completely helpful, since this would require switching to AUX everytime a phone call comes in, unless it's able to automatically switch over. I'm not aware of any that do, but I'm not an installer or keep up with the industry, by any means. This would be the best way in terms of audio quality, though.
Some kits output audio either by interrupting the head unit's speaker outputs while others use a seperate mini speaker that come with the kit. Mute may be handled by either triggering a mute lead on the head unit if one exists or, again, by interrupting the speaker outputs.
I have the CK3100 in my S40, and had to purchase another mute harness that was only sold in UK, that was an additional $100. It's ok, but I'm not satisfied with the microphone's sound quality. I'm always looking for a kit that has a good noise cancellation ability. If anyone knows of one, please let me know.
In my xB, I use the Z2's bluetooth module. It seems ok so far, but I haven't really tested it much, yet.