The following GSM call forwarding codes may be used to enable and manage call forwarding options on iPhone devices.
Unconditional forwarding:
Forward service: All Calls
Activate: *21*phone_number#
Cancel & Deregister: ##21#
Cancel & Retain: #21#
Status: *#21#
Reestablish: *21#
Conditional forwarding:
Forward service: If Busy
Activate: *67*phone_number#
Cancel & Deregister: ##67#
Cancel & Retain: #67#
Status: *#67#
Reestablish: *67#
Forward service: If Not Answered
Activate: *61*phone_number#
Cancel & Deregister: ##61#
Cancel & Retain: #61#
Status: *#61#
Reestablish: *61#
Forward service: If Out of Reach
Activate: *62*phone_number#
Cancel & Deregister: ##62#
Cancel & Retain: #62#
Status: *#62#
Reestablish: *62#
Simultaneous forwarding:
Forward service: All Forwards
Activate: *002*phone_number#
Cancel & Deregister: ##002#
Cancel & Retain: #002#
Status: *#002#
Reestablish: *002#
Forward service: All Conditional Forwards
Activate: *004*phone_number#
Cancel & Deregister: ##004#
Cancel & Retain: #004#
Status: *#004#
Reestablish: *004#