Apple iPhone 4

Find "Keypad"

Press Phone.

Find "Keypad"

Press Keypad.

Choose option

Choose one of the following options:
Divert all calls, go to 2a.
Divert missed calls, go to 2b.
Divert if unavailable, go to 2c.
Divert if busy, go to 2d.

2a - Divert all calls

Key in **21*+447836121121#

2b - Divert missed calls

To select for how long you want your phone to ring before the call is diverted:
Key in **61*+447836121121**the required number of seconds#
E.g.:
*61*+447836121121**5#

2c - Divert if unavailable

Key in**62*+447836121121#

2d - Divert if busy

Key in**67*+447836121121#

Send request

Press Call.
A request to turn on the setting is sent to the network.

Send request

Press Dismiss.