I guess imagine a device where both RIMM and Microsoft developed together where you had the best of both companies in 1 package where it be tablet or phone.
Hmm, lets see. I love my current phone but, I would make the screen wider. Not the phone just the screen.
Also those buttons at the bottom have got to go. I would also push them down a bit farther in the face of the devise.
A better spaced out touch keyboard would also be necessary. Somehow despite having a smaller screen the iPhone keyboard has much more room. I suggest they find a way to get rid of some redundant buttons.
As for camera, 10mp.
Games? Time to link up with a player like Sony and their PSP so you can have really high quality games on the phone. I would assume that the phone could handle it with its current processor.
So basically, bigger screen(phone wouldn't be any bigger though), flush buttons, better keyboard(landscape and portrait), better camera, more high quality apps.