Find "Voice call"
Press Apps.
Press Phone.
Press the Menu key.
Press Call settings.
Press Call forwarding.
Press Voice call.
Select divert type
After a moment 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 alternative number
Key in the required number and press Enable.
Exit
Press the Home key to return to standby mode.