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