ccfj1 many thanks. I had a feeling the microphone was installed there. Unfortunately I have no obvious cutout there on mine so would mean cutting the lining. Don't fancy doing that. I have noticed another possible location and this is using the 'missing' grab handle screw covers right above the driver's door glass.
Did you cut your lining to get the microphone in or was there some blanking plate already there?
Thanks for the info about the connects 2. Unfortunately it does not answer my original question regarding 3100 unit.