In my vehicle I use a Nokia CK-7W bluetooth handsfree system which
automatically pairs when I turn on the ignition and routes calls through a
mic and speaker permanently mounted in the vehicle. There is a button to
answer or hang up a call, and for initiating a call using a pre-recorded
voice prompt to select a contact (cool).
With my Nokia CARK-91 wired car kit I could set the Nokia Car profile to
auto-answer, so calls would pickup after 3 rings. Normal profiles would ring
and go to voicemail if not picked up.
On WM5 I can see how to set the auto answer to 3 rings or so, but not just
when paired with the BT handsfree.