I'm as frustrated as you mate..... It appears the BT Stack will ONLY work with Stereo BT headsets - not even a Stereo audio receiver with A2DP, such as the Anycom BAR-10, which I love and use all of the time with my Sony BT dongle and looks like I will need to continue using it.
Another shortcoming is one can not skip songs, but only play & pause - why would they disallow that feature as it can/is process commands back upstream with the play/pause buttons....
All in all, I am very dissapointed with the implementation and I too want the capability to tether to my phone for 3G Internet access - if they would only enable that feature, it will grow their market share as others would like to leverage that feature, as well.
Furthermore, there is a thread going on below, where this also being discussed:
http://discussions.apple.com/thread.jspa?messageID=9651872#9651872