Tap Phone.

Tap Keypad.

Tap the menu icon.

Tap Settings.

Tap Call.

Tap More settings.
After a moment the current settings are displayed.

Tap Call forwarding.

Tap Voice call.

The current settings will be displayed.

Tap one of the following options:
Always forward

Forward when busy

Forward when unanswered

Forward when unreachable

Key in the required number and tap Enable.

Tap the Home key to return to the home screen.