Those users who complaied at lenghth about the fact that the Treo 600's screen stays on througout a phone call should be happy with the 650 in this regard.

The 650 dims down in two steps during a conversation. First, after a short period of inactivity, the screen dims a bit, but the keyboard remains lit. Then, if another period of inactivity passes, the backlight is completely turned off as well as the keyboard lighting.

What helps in this is that the 650's screen is the reflective nature of the transreflective screen. When the backlight is completely off, you can still see the screen if there is any light around you. The screen basically becoms like a regular (albeit darkish) LCD with no backlighting. This allows the backlighting to be off without the phone looking totally confusing as would be the case if the screen were completely off (the 600 could not do that). IMO, this would have been a bad design decision for the 600, but on the 650 this works very nicely.

Another nice touch is that once the screen is dimmed, touching it would ONLY reverse the dimming, but won't have any other effect. This eliminates the possibility of performing a function you don't intend or even end the call by accident because you couldn't see where you were touching on the darkened screen. So it's taken as a wake up touch only. A smart design choice, IMO.