I Stream music from my Droid X Via Bluetooth All the time. I use Pandora or Music off my SD card. I Have a Cheap Sony Xplode deck that I picked up cheap and had installed for under $300 just for this reason. When I have BT turned on and I start my car, a phone icon and a music icon show up on my Sony Radio and then i switch to BT Audio as my source.
So I am assuming that this is also going to work on the Galaxy S3 or at least I hope so Becuase I also Pre-ordered one 2 weeks ago through VZW. I have also Hooked up feature phones of my friends the same way when they had music on their phone that they wanted to hear. This option is also usually Clearer and better sounding audio then an AUX cable( at least on my radio with my DX)
Steps are usually pretty simple. The receiver has to be put into discovery mode. Then you turn on your BT on your Phone and it should discover the Radio. Then you just pair them and go.
Hope this helped.