When fixed dialling is turned on, you can only call selected numbers and do emergency calls. Incoming calls aren't affected.
Press the menu icon.
Press More settings.
Press the required SIM.
Press Fixed dialling numbers.
Press Enable FDN.
Key in your PIN2 and press OK. The default PIN2 is 0000.
Press Disable FDN.
Press the Home key to return to the home screen.