Find "Voice call"
Press Applications.
Press Settings.
Press Call settings.
Press Additional settings.
Press Call barring.
Press Voice call.
Change barring password
Press the Menu key.
Press Change password.
Press Old and key in your current barring password (default is 0000).
Press New and key in a new barring password.
Press Cofirm and key in the new barring password again and press OK.
Exit
Press the Home key to return to standby mode.