Locking the screen on the mogul

[mmhhtc]

How do I lock the screen a la the Treo 650? When a call came in on the Treo, I got a notification but the screen was locked until I hit the center button on the 4-way pad. I rarely (if ever) picked up a call or activated a program whilst the Treo was in my pocket. But the side button on the Mogul is in the wrong place. I often find I have made a few calls, activated some programs, and maybe even done some editing all while the phone was in my pocket. Suggestions would be greatly appreciated.