replacing onstar in 2002 caddy

I have a 2002 deville and I'd like to replace Onstar with a bluetooth to my Cell phone.  I now about the motorola that sticks on the dash etc. but what I really want is to put something in the car that would tie into the data bus, radio, existing onstar microphone and steering wheel control.  Anybody have any advice? 

If nobody has a solution is anybody interested in designing a solution.  We could market it as UnStar.