As one who has worked in IT since before dumb terminals and has seen such innovations as teletype terminals and the 3270, the industry is never going back.

OTOH, there is a convergence and it is due to Moore's Law. In about a year, there will be 2GHz processors that will fit in small devices and throttling them down in standby mode to support basic phone functions will be production ready. At that point, it will become a question of what form factors will sell.

I would predict that there will be 3 inch and smaller screens for dumb data phones which are designed for voice functions and an occasional side trip to Wikipedia, Google News, or ESPN. Smartphones will cluster around a 5 inch screen that can fit in a shirt pocket and will be capable of running PC (x86) software. Some netbooks will converge (possibly with eReaders) around a 7 or 8 inch screen while others merge with lightweight laptops around a 12 inch screen.