Top left button is the Keylock. But, pressing any key or moving the trackball will make the screen come on, but not allow you to do anything. This is fine, but if its in your pocket, the screen will probably stay on as the trackball will keep being moved around.
Originally Posted by Ronin_81
The top right button however, is the mute/sleep key. Holding down this button will put the phone to sleep. The only button that will put the screen on is the escape key and the mute key. The only thing that will unlock it is by pressing the mute key again. This will be what I use. When it puts the phone to sleep, from my understanding, nothing is on, except for the radios, so you will still be able to get messages and calls, while saving power.