Yeah, it's possible. I did this in my Lincoln (with Ford's Sync system) with my iPod Touch. You basically have to "pair" the car's Bluetooth with the device. The car then recognizes the device as an audio source. My car has a setting for Bluetooth Audio, so I set it for that and then set the device to play the music. My system allows me to use the steering wheel controls to adjust the volume and skip tracks, but I can't use the car's voice control to control the iPod. Every car system is different, so you should consult your owner's manual for the proper connections and use.
In spite of the BT connectivity, I still prefer to connect my iPad or iPod directly to my car's music system using a USB cable. By using a cable, I can sort the music by genre, artist, song, etc. as well as control the whole thing using voice commands.