Here’s a helpful, straightforward write-up on (also known as network service restriction codes). What Is a Call Barring Code? A call barring code is a numeric password (usually 4 digits) required to activate, deactivate, or check the status of call barring —a network feature that restricts certain types of outgoing or incoming calls on your phone.
Call barring works on the network level (via your SIM card and mobile carrier), not just on the phone’s software. This makes it more secure than airplane mode or do-not-disturb, because even if someone swaps your SIM into another phone, the restrictions remain. GSM networks use standardized service codes (also called MMI codes ) starting with * and # . You dial these like a phone number. The most common ones are: call barring code