Walt Mossberg is using the iPhone in preparation for a review of the white-hot handheld. As anticipated, the biggest challenge he is facing is the keyboard. The touch screen keyboard supposedly uses technology that makes typing on the iPhone easier and faster than on a conventional keyboard. Walt's not so sure. Neither am I. I believe that most people need the tactile feedback provided by a keyboard while typing. Of course, people will grow accustomed to using the touch-screen, but Apple may face a very high hurdle with the keyboard issue as it readies the world for June 29.