I really liked what Craig had to say about a single device not necessarily being for everyone. Craig mentions his own need to enter data into a device which just isn't very reasonable with a smartphone:
The one task that Steve does not mention at all is entering text into the device. While the Microsoft Smartphone is a pretty nifty concept, since it has neither a touchscreen nor a thumb-keyboard, it doesn't allow for much, if any, text entry (short of the old-fashioned numpad-multiple-press approach). It has predictive word guessing, but if it's the same as on the Pocket PC, that's of minimal help.
Like Craig, I don't want to try keying in text with a phone keypad... it's just way too painful and pokey. Even word completion software falls short in this regard. I question how many features of a smartphone the average person will actually use if text input is difficult. If so, it's quite likely the PDA functions of smartphones won't be getting much use. Doesn't this make the smartphone more or less a view-only data device? I don't want a view-only data device. I want the ability to enter my work time, notes, phone numbers and decent chunks of text in a reasonable fashion.
My daily device must also have a large enough screen to be legible for seeing what I'm writing or for reading e-books. If a smartphone screen is too small, long-term viewing becomes painful. If a screen is too large. the device doesn't work as a compact phone. The Treo 600 may be great for mobile phone and data purposes, but I'd go crazy trying to read a decent lenght e-book on that small, low-res screen.
As for cost and durability, I'd much prefer a separate low-cost mobile phone to bring on cycling trips. That way I needn't worry about destroying a $600 smartphone if I were to crash, or ride off the road into the creek. :-)
This all leads me back to a PDA. Now, I'd be very interested in a slim PDA with wireless capabilities and a nice screen. Something along the lines of a Tungsten E or T3 with built-in WiFi and Bluetooth networking would be perfect.
I can use WiFi in the house or at hotspots and Bluetooth might also be attractive with a Bluetooth phone (if I decide that's needed someday). This is where I believe the world of PDAs will naturally go, because pretty soon, wireless technology will be cheaper to include rather than exclude.
Where will the future take the PDA, mobile phone and smartphone? I don't really know. If we're to believe the pundits of late, PDAs are supposedly doomed. I believe there are many others like me, who don't want or need a smartphone but do want or need a PDA. I just hope that in the dash to make devices for the supposed "millions" who are clamoring for smartphones that we PDA users aren't forgotten by device makers.