I just used an iPhone on a cross-country trip. There is poor access west of Williams, AZ.
It was "reasonable" 98% of the time.
If I had a device with 4x the display size of an iPhone such as an Apple Tablet Not Nano, and with copy and paste capability, and a third pane of keyboard with symbology, and buttons to go forward and backward characters while editing, I could have replaced my Powerbook.
If it had 802.16 Wimax (or IBM's new microwave protocol) and access to such a network with 80% the coverage of ATT's awesome EDGE (built for CIA/NSA), then I could have received, marked up, and resent attachments to my co-workers with aplumb too.
EDGE is ever present in this country (and others). It is slightly faster than dial-up on its best days.
I expect an office like suite on an iPhone like device (with larger/dual displays) next year. It has the capability to replace traditional "personal computers".
Wimax is broadband on the run.
Rocketman
Runner.