I have experimented with this quite a bit, and I downloaded an application for Android that allowed me to use the Bluetooth connection in the car on my E86 as a speaker.
DON'T, the sound quality is awful.
Instead, I now use one of these:
http://www.amazon.co.uk/Nokia-Clip-On-Bluetooth-Noise-Blocking-Headphones/dp/B00HRUGPDM/ref=sr_1_1?ie=UTF8&qid=1393849722&sr=8-1&keywords=Nokia+BH-121
It simply plugs into the AUX port with a really short lead. You can then just turn it on as you jump into the car, and your phone will pick it up automatically and use it as a speaker. I've combined this with a Qi wireless charging phone cradle and I can now just drop the phone in and go, without having to try to plug wires into the phone every day.
From what I can see, the Nokia device above works with all models of phones, not just Nokia/Windows phone.
Mike.
P.S WOOT 200 posts.