I have the Samsung Infuse 4G with the car navigaiton mount. The mount has a 3.5 mm jack for lineout. The audio gets to the 3.5 mm jack via the micro usb connection, since that's the only connection from the phone to the nav mount. As long as I'm using Samsung's Car Home App, I get audio out to my truck speakers. I like the fact that I can just put the phone in the dock without having to plug anyu cables in (since the charger and audio cables stay plugged into the nav mount), because most times I get in the truck, I don't want to fiddle with cords, I want to pop it in the dock and go.
The only two problems are
1) Samsung's Car Home App has zero customization. I mainly listen to podcasts downloaded with Google Listen, which do not show up in the stock music player, which is the only media option available in the Samsung Car Home App.
2) I rooted then flashed the Infused custom ROM, and the Samsung Car Home App was no longer available for the phone. I went back to stock, and it's available again.
So- does anyone know is there a way to choose line out as an audio output outside of Samsung's Car Home App? I've tried other car home apps, without luck.

 

I agree, the mount is less than ideal, I actually modified mine a little so I could remove the phone from it easier. I probably would go with a universal mount, except, as I said above, I want a one step process: A) pop the phone in it's holder and have it play through the truck's speakers. Any universal mount will require me to: A) place phone into it, B) Plug power cord in to micro usb port on phone, C) plug in an audio cord in to 3.5 MM headphone jack.
I also am not a big fan of the Car Home, but it seems to be the only way to get audio though the micro USB port, unless I'm missing something.