Personally, if I were leading the design team.. I would-
-Make the left and right side of the screen (where the buttons are) slide out in opposite, respective ways
---- this would keep the size-in-the-pocket down, look more sleek, and appeal more to the masses
---- having of the sides slide out could reveal a camera
-Make the screen a touch screen, appealing to those that like touch screens
---- it'd ride off the fame of current touchscreen devices, like the DS, iPhone, etc
-Make it a little more rounded with a few color options, one of those definitely being a black/gloss black
---- it'd have to be less than an inch thick or else it'd become absolutely unappealing
I'm sure I could think of other stuff, but that's where I'd start if I were to design this thing.