If you have a MY2012/2013 car and enable the firmware beyond version 0770, you lose the ability to make telephone calls via Bluetooth. The car expects you to use the built in SIM only. To remedy this, enable the ‘Make calls using’ function via the green menu:
Enter the Hidden Menu
Check “NAD operation mode”
Press CAR to exit the hidden menu
Reboot the MMI
Once the MMI reboots you will be prompted as to which device you’d prefer to make calls on – either MMI or your Bluetooth telephone. Select Mobile Telephone. Once selected a second reboot is required.