If you own a GSM phone (most of us do as it is used in many countries), then there are several codes that can be entered to tell the network how to handle incoming calls and more. These codes are not really considered secrets, but they are poorly documented by service providers.

Not all codes given below are supported by all service providers. But, there is no harm in trying a code. You can know which ones work and which ones don’t by a confirmation or rejection message.

Call waiting

  • Activate call waiting *43*#
  • Deactivate call waiting #43##
  • Check status of call waiting *#43#

CLIR: Presentation of one’s own number to the to the called party

  • Activate CLIR **31#
  • Activate CLIR for the actual call *31#number
  • Deactivate CLIR ##31#
  • Deactivate CLIR for the actual call #31#number
  • Check status of CLIR *#31#
  • Change call barring code **03*OldCode*NewCode*NewCode#
  • Change call barring code **03*330*OldCode*NewCode*NewCode#
  • Change PIN code **04*OldPIN*NewPIN*NewPIN#
  • De-register all call diversions ##002#
  • Activate unconditionally divert all calls *21#
  • De-register unconditionally divert all calls ##21#
  • Deactivate unconditionally divert all calls #21#
  • Check status of unconditionally divert all calls *#21#
  • Divert on no answer to number and activate **61*number#
  • Activate divert on no answer *61#
  • De-register divert on no answer ##61#
  • Deactivate divert on no answer #61#
  • Check status of divert on no answer *#61#
  • Divert on not reachable to number and activate **62*number#
  • Activate divert on not reachable *62#
  • De-register divert on not reachable ##62#
  • Deactivate divert on not reachable #62#
  • Check status of divert on not reachable *#62#
  • Divert on busy to number and activate **67*number#
  • Activate divert on busy *67#
  • De-register divert on busy ##67#
  • Deactivate divert on busy #67#
  • Check status of divert on busy *#67#
  • Check status of barring all outgoing calls *#33#
  • Activate barring all calls **330*code#
  • Deactivate barring all calls #330*code#
  • Check status of barring all calls *#330*code#
  • Activate barring all outgoing calls **333*code#
  • Deactivate barring all outgoing calls #333*code#
  • Check status of barring all outgoing calls *#333#
  • Activate barring all incoming calls **35*code#
  • Deactivate barring all incoming calls #35*code#
  • Check status of barring all incoming calls *#35#
  • Activate barring all incoming calls when roaming **351*code#
  • Deactivate barring all incoming calls when roaming #351*code#
  • Check status of barring all incoming calls when roaming *#351#
  • Activate barring all incoming calls **353*code#
  • Deactivate barring all incoming calls #353*code#
  • Check status of barring all incoming calls *#353#

Go here to see the original:
Most Common Codes Of Any GSM Network!