Interesting article from bargainpda.com entitled:
"Does the palmOne Treo 650 Replace Treo 600? Not Exactly."

http://www.bargainpda.com/default.asp?newsID=2273

"palmOne gets a little upset when people call the Treo 650 just an "evolution" of the Treo 600. They insist that it is indeed a step up the ladder and not just a leg lift towards that next step. If you look at the devices side-by-side (as pictures in this article show) then you'll probably agree that the new keyboard and screen alone do make for a good argument this is not just a few features slapped onto an existing device and then called new. So having called the Treo 650 a revolutionary and new device which is clearly better in every way than the Treo 600, we can assume the 650 will replace the 600 and production of the 600 will end now, correct? Incorrect...."