W800i using stereo out and bluetooth headset

Here is a hypothetical scenario:

If I am using the W800i in my car, with the optional stereo jack attached to a cassette adapter to play music in my car, and I also have a bluetooth headset, how would the W800i handle phonecalls while I am listening to music through the stereo jack? I.e., would it pause the music and transfer the call to my bluetooth headset? Or would I have to disconnect the stereo jack and pick up the phone by hand? Has anyone tried this?

I actually don't own a W800i, but I am thinking about buying this instead of an ipod nano. Thanks in advance for any help!