Why do Blackberries and other handheld electronic devices have QWERTY keyboard arrangements? QWERTY is for touch-typing, which relies primarily on muscle memory. If you ask me (a touch-typist) where a particular letter is on the keyboard, the fastest way for me to get the answer is to move my fingers as though I'm typing, not to recall the location from visual memory. But on a handheld device, you can't do standard touch-typing, so you're back to hunt-and-peck, which works just as well and probably better with the keys arranged in alphabetical order.
(Of course, if you use a Blackberry often enough, you'll start to develop muscle memory in your thumbs -- but this will be distinct from the muscle memory of touch-typing, and could develop as easily for an ABC keyboard as for a QWERTY keyboard.)