This requires that your car has the SA620 = SES module installed. My car is a Feb.2002 e39 sedan (i.e. w/o universal phone cable installed).
Now, all you have to do is to re-pin 10 of the SES connector pins to an empty 54pin housing (got mine from AUDI p/n 4e0-972-144) and plug it into an SA644 BT ULF module (see diagram below). One additional pin (AUDI p/n 000-979-010) is needed for the pairing button. BT antenna (p/n 84506928461) and short FAKRA connector cable (p/n 84320138217) are cheapest from BMW.
Don't forget to disconnect (or remove) the old phone (mine was V50) components in booth and center armrest (unplug 2 connectors).
Use NavCoder to enable SES in ULF if neccessary.
...there you go!
Ronny
Oh, AND big THX to
ccfj1 for his
post!