It's like tablets.  Limited audience, but competition is fierce in this market and every provider wants to have a complete solution so they all make one but I don't think there will be a push to sell them.  They are just there if someone wants them. 

The problem we are having is to get something small like a phone in your pocket but give it the functionality to do work on it.  The industry tries to find a workable balance but there really isn't any.  You can't get a full size keyboard and decent sized screen and fit it in your pocket. 

These days, they are shooting for that "paperback book size" rather than the encyclopedia size of a regular laptop.  But if you have to carry it, you might as well carry the big one that is full featured over the small.

I think eventually an iPhone type device will be powerful enough to act as a full featured PC or Mac.  But it'd have to be something that you could pop into a cradle and use a regular keyboard, mouse and monitor.  Apple is getting close.  But even they have a while to go yet before the hardware innards are good enough to actually run like a real computer.