To lock the keys manually in the home screen, press the left selection key and *. Or press the power key briefly, and select Lock keypad.
To unlock the keys, press the left selection key and *.
The keypad of your device locks automatically to prevent the keys from being accidentally pressed. To change the period after which the keypad is locked, select Menu > Ctrl. panel (or Settings) > Settings and General > Security > Phone and SIM card > Keypad autolock period.
When the keypad is locked, you can still answer to incoming calls and the calls may be possible to the official emergency number programmed into your device.