The idea is to use the proximity sensor to detect if the phone is inside a pocket.
Somehow to replace the function of the lock slider with an automatic keylock function so the phone automatically locks when the proximity sensor is being covered, and automatically unlocks when the sensor is uncovered again.
Also, When you make or receive a call, the automatic keylock deactivates.
If you are or was a symbian user, you may recognize PocketSensor that does the same job...
Anyone can do a little applet to allow this handy "feature"?
Discussion: http://talk.maemo.org/showthread.php?p=549875#post549875