To activate/deactivate this lock one needs a special secret code that is not available to the end user.
Here is how to activate the menu:
<**< Lock to Network? if pressing yes you have 5 attempts to enter NCK.
<**<< Lock to Network subset? if pressing yes you have 5 attempts to enter NSCK.
Warning: Your phone can be locked to a service provider FOREVER by doing this! If an invalid code is entered all five times, the menu will exit and be deactivated! Any further attempt to activate the NCK/NSCK lock Menu will result in the response "Not allowed"! However the NCK/NSCK lock can be recover through a direct clearing in the EEPROM.