As others have said, there are several ways you can do this.
1. Aux cable is probably the best way if your head unit has an aux input. This is basically just a cable with a headphone plug at both ends. You can get them anywhere that sells electronics for about 5 bucks or less.
2. Bluetooth is the cleanest way since it is wireless, but you need to have a head unit that supports A2DP.
3. Cassette adapter. Cheap and easy if your head unit has a cassette player. These have been around since the days when everyone had those portable CD players.
4. FM transmitter. These can be a little expensive for one that works halfway decent (around $50) but your only option if none of the above options will work for you.
You can't do that. We're not talking USB cable, we're talking the headphone jack. If your car stereo has an aux-in headphone jack, you want to use a cable and connect it that way. The only reason it worked with the iPod Touch is because they have special programming in the stereo for them.
Seems like HTC SCREWED UP BIG TIME AND SHOULD HAVE TAKEN A PAGE FROM APPLES PRODUCT
THIS is wAY TOO COMPLICATED IN ORDR TO LISTEN TO A FEW TUNES IN MY CAR
I disagree entirely with your statement; I could argue that Apple screwed up big time by using a proprietary connector, and I would also be wrong. They are different products, you need to look for a solution that works with the product you own. Maybe in the end, your best option is to go with an Apple product.
Have you considered going to a shop and inquire about adding an auxiliary stereo jack to your sound system? in some models is possible.
I am currently using my phone thru my car stereo to listen to music. I bought a male to male plug in from radio shack. I think it was 8.99 for 6 feet took about 2 minutes to connect to the back of my stereo and then routed through my dash and up and behind the pillar and then to my phone.
Works great and YES...the headphone icon is displayed on the phone.