You
can set the keypad of your phone to lock automatically
after a pre-set time delay. You can set the delay time
from 10 seconds up to 60 minutes; when the time is up,
the keypad locks automatically, preventing accidental
key presses.
Press Menu, and select Settings,
Phone settings and Automatic keyguard.
Select On and set the time delay from 10 seconds
to 60 minutes. To deactivate the automatic keyguard, select
Off.