i use my htc mogul in my car. you should have gotten 2 y plugs in your box with the phone. one is the usb end for the phone and the other has a usb female to plug in your car charger and the other end has a tiny stereo (walkman style plug). it's not the standard 1/8", but a smaller (i-phone/pod) plug. i got a scosche adapter kit that had all types of adapters to connect on airplane, smaller stereo, and more.

if i had seen the one dynamic sound posted i probably would've just gotten that, but you can't run the charger at the same time. sometimes it'll put noise in and create a ground loop, so if you have a good battery and one charged on backup you can listen for many, many hours at a time without having to run the charger at the same time.