I have a file "pin" in /etc/bluetooth, containing my PIN, nothing else, only one line with "123456" (here a fictive PIN).
Then I have a special script to give the PIN to the mobile phone (I do not use the script out of KDE), I called it /usr/local/sbin/pin and it contains these lines:
I made it executable with "chmod +x /usr/local/sbin/pin".
Then I changed the file /etc/bluetooth/hcid.conf in this way:
# Default PIN code for incoming connections
With these modifications I have no problems with three mobile phones, kbluepin not always worked for me ...