Some people may not know that there is a keylock function on Windows Mobile smartphones – you just have to press and hold down the Hang Up button (the button with the red phone icon).
It works no matter what menu you happen to be at the time, except, of course, when you’re making a call.
When you’re on a call, you can also put it on hold by pressing the Call button. Press the Call button again to resume.
Note: The tricks only work on certain models of smartphones, and not on Pocket PC (PPC) Phone based Windows Mobile.