Well I gave what I described a shot on my Treo 800w with my Scala-500 and it didn't work. Used to work on my HTC Apache with the same headset, but that was Windows Mobile 5.0. Maybe they've change the default action for the bluetooth button or maybe my headset is not fully compatable with the 800w.
My voice command is not working with my bluetooth either. What the crap! I've got to many issues of my own to help you man!