What a great topic!
And what interesting results this should produce.
I think that PDAs can and could play a very useful role in the classroom, but not as a teaching aide.
We all thought that PCs and laptops would revolutionize the classroom but when we look today they are still rarely seen outside of the IT class.
In terms of a Mobile Device in every student's hand delivering the content of the lesson, the screen is surely too small for too small to spend upto an hour staring down on. I think an electronic whiteboard at the front of a class holds more benefits; space for information and the right height so people don't get strained necks from looking down.
But, swapping the exercise book, the notes, the planner for a Windows Mobile 6 Standard device makes sense.
A centralized timetable per student with daily on screen reminders to show which lessons/lectures are to held that day, network based, text entered notes, backed up nightly and available for the teacher/tutor to mark, homework/coursework as tasks with evening on screen reminders of due dates and then the use for online research.
Wireless hotspot onsite plus a data only plan out of hours to keep costs down.
This question has certainly got me thinking about it!