The IPhone - considering how small the screen is - has amazingly clarity, and is far far more usable than someone who doesn't have one would generally be inclined to credit. I can remote into my work system from my IPhone and monitor processes seamlessly. I can easily view train schedules, etc. Now having said that, I would not want to view technical data with any real amount of technical drawings embedded on the IPhone - I'm going to want something larger. I'd suggest one of the inexpensive Netbooks, myself.
There are a number of third party apps that let you transfer, store and view PDF's on the I-Phone - without jailbraking. I use File-App (which used to be FileAid) which works well.
But don't get an IPhone looking for a stellar PDF viewer - get one because you need a decent PDF reader, a decent GPS, a decent phone, a decent mobile Internet browser, a decent calendar system, and any combination of about 100,000 special purpose apps ranging from an application to allow someone with Celiac to choose appropriate food while eating out to a zombie shooter to news to a kazoo - all with an absolutely stellar interface to tie it all together which really is so simple a caveman can do it - or my 5 yearold.
I've been in technology a long time - and I can't recall the last time a piece of technology lived up to and exceeded the hype as the IPhone does.
If I had to get a PDA sized device for this purpose, it WOULD be my only choice. But I think there are better choices.
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