Samsung SCH-R250ZRAMTR - Manual (Page 135)

Changing Your Settings 131
Auto Device Lock
Auto Device Lock lets you set your phone to automatically lock itself
when the display backlight shuts off.
Change Lock
Change Lock lets you replace your phone’s default lock code (the last
four digits of your phone number) with one of your own choosing.
It is advisable to change the default lock code to a secret code for
security purposes.
When you select Change Lock, your are prompted to enter the
current lock code followed by entering your new lock code, and then
re-entering it, for verification.
Note: Your phone does not allow you to view the lock code for obvious security
reasons. If you change the lock code, be sure to write down or memorize
the new code.