Dave Hornik, a veteran Sand Hill Road VC and industry observer eliminated books and used his iPhone in Europe on his summer holiday, something I have done and also not done.
First off, for AT&T Customers who are heavy business mail users like I am, the iPhone is NOT a useful replacement for the RIM BlackBerry with International Roaming as I’ll blow through 100 megs in a few days just with email in an always on mode on the iPhone. A better option I’ve found is the unlocked Nokia E71-1 (the European variant with Euro 3G) and Mail For Exchange, plus a local SIM card with Data if I want a device for mail and light surfing. The E71 and the Berry blow away the iPhone as well due to the keyboard.
A second option is a Novatel MiFi (unlocked GSM Model) and a iPod Touch.
If you really want to use the iPhone, do as David and I both do. Don’t make calls over it (unless you’re in a WiFi hotspot and use client Truphone or SKype or Fring to make your international calls) or as I like to do, I use my E71 and either call via Truphone Anywhere or buy bundles of international calling (as T-Mobile offers in the UK 120 minutes to the USA for 11 dollars and change and my local minutes are not consumed)
As for data, I used the iPhone for many of the same things Hornik did, but in reality for all but two weeks out of six I had it turned off when I had a rental car with GPS. Candidly, most of what I needed to know-like how to get from place to place was there, and the only time the iPhone or even Blackberry maps via Google was used was when I was walking around.
As for books-guidebooks especially, I find too many local books in book stores that are full of information that’s not easily found the first time, online. For me, places like winery’s with full restaurants, rooms for rent and more are not all in one place online. I’m sure the same applies to other categories that are more niche than generic, which is where the travel guides tend to be that first make it online.
At the end of the day, it comes down to three parts. The service, the app and the content, not the device alone, that will make for the end of books as we know it.