When you set-up the keyguard on your treo 650, it will lock your phone after it goes to sleep - depend on the setting on the preference - to avoid any accidental keyboard pressed.
but when you wake the phone up, the lock still active, and you need to press the center of the d-pad to activate it.
so it need two step for the treo to be function normal, first waking it up by pressing the red phone button, then pressing the central button of d-pad.
btw, there's a shortcut for it, so you only need one step to wake your treo up.
it's done by pressing the alt button (the blue button) with the red phone button.
your treo 650 will instantly active.
source: id-palmOS milis.