This feature allows you to bar incoming and outgoing calls using a four-digit password selected by you. This is a security measure to prevent the possible misuse of your cellular phone. This feature will work only if the Call Divert feature is de-activated. You can selectively bar all incoming calls or all outgoing calls as well as outgoing ISD calls. You cannot selectively bar outgoing STD calls. This is a handset dependent feature. Refer your handset mannual for more details.