I can only seem to use the back button (key lock) to lock the screen when I am on the default splash screen. Is there anyway to change the behavior so that the key lock will engage after a certain amount of time regardless of which portion of the phone's menu you are in? Or, can you use the key lock in any screen?
Unfortunately not. This is the feature of that button per the userguide on page 8, the Back Arrow also doubles as a Lock Key but only from the Home screen. You'll have to hit End, then back to lock the screen or buttons.