That's device convergence for you. It's interesting how many different start points seem to be heading towards the same end point.

There's the thread of taking the desktop UI and software and trying to squeeze it down to a mobile format (like Origami, or Tablets to a lesser extent). Then there's taking the phone UI's and trying to expand them to be more capable in some of their functionalities. Or taking a PDA software and trying to expand that. Or starting from a rather new system (like Apple did with the iPhone [although it shares part of the code with the desktop]).

Ultimately... I would say that the device physical size becomes the determining factor. There is a clear need for something that you can carry around with you all the time - like your phone currently - and something a bit larger that will enable efficient working, like a laptop.

Personally I'm skeptical is there really a viable niche between these two form factors. I do see small laptop and large laptops, but I'm not sure about the hole between the phone and a small laptop. The UMPC's, like Samsung Q1 are basically too big to be pocketable but too small to be actually usable as laptop replacements.