Samsung Infuse works in car when connected via USB
I also got Samsung Infuse recently, and i also had the same problem, mp3 player does not work when connected to car via USB.
Now i found a solution for that problem. Please follow the steps below,
Settings -- > Applicaitons --> USB Settings -- > Development -- Uncheck the Debugging Option
Now switch off your car stereo, connect your phone to the car via USB, and select
'Mass Storage' option when prompted.
Once it is connected, now switch on the car stereo, and it should play the music.
i tried the above steps and playing music in the car via USB.