so you have an RD4 head unit, whith the small screen, and im guestimating its an orange display
has the head unit got a "TEL" button if yes, then next thing is to remove the interior light and see if theres a microphone and its wiring there
if the mic and wiring are there, then you need to remove the head unit and see if the bluetooth pack is still there
if theres no tel button, then its not OE bluetooth, if its there but no mic etc, then its probably a replacement head unit
when using the mode or tel buttons does it give you the option to pair the phone
when the later RD4 with bluetooth pack was introduced they fitted it with a small colour screen, but the later orange screens were also used on models once the later orange screen was introduced and the colour ones are few and far between and were fitted more to the coupes (the earlier orange screens fail in heat and extreme cold)
i had the RD4 with small screen, and i upgraded and modified to the RT3, this has built in phone and cd based sat nav and large 7" colour screen, the downside being it does not have bluetooth capability and unlike the RD4 you cant fit a parrot or any other aftermarket bluetooth kit, and ive always kept my tom tom sat nav for the speed cameras