Old school iPhone Bluetooth

[kaentae]

So I'm attempting to set up some kind of Bluetooth system for my car for all those long journeys sat in traffic on the way to and from work, or uni, or just generally wherever. However my current car stereo does not have Bluetooth.

I currently use a cassette adapter to play my MP3's through my car stereo. I have recently bought the Griffin Window Seat for my iPhone 3GS, and an issue for me would be having lots of cables coming and going to my iPhone that is docked on my windscreen. Also with my current setup I don't have a way of receiving handsfree calls and listening to my MP3's at the same time. (I should probably mention I already own a Bluetooth headset.) So I after searching on the internet I came across this:

http://tinyurl.com/bluetooth-to-cassette

It's the Brando Bluetooth cassette adapter. So my question is to anyone that understands Bluetooth slightly better than I do, will this allow me to listen to music AND make hands free calls through my cars current audio system? Will I be able to use the microphone that is current in my Bluetooth Headset as an audio input and use the cars speakers as output. So basically having both the cassette adapter and the headset connected to the iPhone via Bluetooth?

Sorry if that sounded confusing, any help would be greatly appreciated. =D