It all comes down to whether the Bluetooth chip in the 6000W supports the Headset or Handsfree profile. It most likely does, but as I stated in my previous post, I highly doubt anything like this would work out of the box.
In fact, I've only seen about 3 people on these forums state that they got a 6000W, so if you want to do something like this, you might have to write/hack some software yourself unless someone knows of some other project going on.
There is a thread somewhere around here about using a particular GSM CF card to turn other Zaurus models into a mobile phone.