Find "Phone lock"
Press Menu.
Scroll to Settings and press the Navigation key.
Scroll to Security and press the Navigation key.
Scroll to Phone lock and press the Navigation key.
Turn use of phone lock code on or off
Key in the phone lock code and press the Navigation key.
If it's the first time you use the phone lock code, you need to key in a phone lock code of your own choice.
Exit
Press Disconnect to return to standby mode.