[AlexAuran]

You can actually use the headphone jack to create a simple wired car kit. I use a 1/2" to RCA adapter plugged into my after-market head unit. The caller can hear me fine, and the caller is heard through the stereo.

The interesting thing is that with the TP1, the mic would pick up the sound from the speakers so the caller would be able to hear themselves creating an echo effect, but HTC has done something to correct this feedback with the TP2. I encourage everyone to try this or something similar, I've had nothing but good experiences.