Lock the keys
When the device or keypad is locked, calls may be possible to the official emergency number programmed into your device.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 > Tools > Settings > General> Security > Phone and SIM card > Keypad autolock period.
To lock the keys manually in the home screen, press the left selection key and the function key.
To lock the keys manually in the menu or in an open application, press the power key briefly, and select Lock keypad.
To unlock the keys, press the left selection key and the function key.