You can only delete ALL phones - to do this...

Hold in the pairing button
Turn ignition key to position 1
Release button after a further 3 seconds
BLUETOOTH PAIRING is displayed
Press pairing button again for a further 10 seconds until you hear 3 beeps
PAIRED DEVICES DELETED will appear on the MID or Bordmonitor
Turn key off

However, I had the same issue with a full SMS pool in the Bluetooth ULF - all the previous owners SMS's were there - I got pretty much their life story, their affair(s) , the kids phone numbers etc etc. Rather worrying really. I spent about an hour deleting ... some seemed to come back after being deleted, but I kept going and eventually they all disappeared.

Now, oddly, when I paired my wifes phone, I get loads of SMS loaded onto the car from 'somewhere' but they are not on her phone or her SIM which is really odd. So I haven't got her phone paired and I don't have the problem.

Hope this helps some.

M.