Find "Voice call"
Press Phone.
Press the keypad icon.
Press MORE.
Press Settings.
Press More settings.
After a moment the current settings are displayed.
After a moment the current settings are displayed.
Press Call forwarding.
Press Voice call.
Select divert type
The current settings are displayed.

Press one of the following options:
Always forward
Always forward
Forward when busy
Forward when unanswered
Forward when unreachable
Divert calls to voicemail
Key in (prefix) 5 (your phone number) and press ENABLE.
Return to the home screen
Press the Home key to return to the home screen.