Just some more details...
The P900 found the handsfree ok, I entered the passcode and it bonded ok. However, the handsfree in the car does not pick up the P900.
I used a Nokia 6310 as well as a T68i which bonded fine without any problem.
For example with the T68i, I did the discover, get it bonded. Then I can just go into paired device and select the handsfree and connect it.
I have tried to send the phone number from P900 via bluetooth to the handsfree (to inital some sort of communication) but it also failed...