I'm not sure if there were "experts" of the same caliber calling the iPhone impossible. In fact, I don't recall anybody saying it was impossible, but would like to find out more.
I remember a ton of doubt, after launch, that it would be successful, but those people weren't really experts.
Here’s one example. Apparently RIM’s employees collectively thought it was impossible (to achieve the stated battery life); I think they count as experts:
> RIM had a complete internal panic when Apple unveiled the iPhone in 2007, a former employee revealed this weekend. The BlackBerry maker is now known to have held multiple all-hands meetings on January 10 that year, a day after the iPhone was on stage, and to have made outlandish claims about its features. Apple was effectively accused of lying as it was supposedly impossible that a device could have such a large touchscreen but still get a usable lifespan away from a power outlet.
The comments summarized in that article seem to no longer be available, but I have a hard time believing the summary is accurate. When the iPhone was released, there were already PDAs on the market with screens the same size or bigger.
The devices at the time with larger screens were larger, heavier devices that had shorter battery life. Nobody made a pocketable device with a screen that size.
I had an iPaq at the time, had maybe 4 hours battery life, and that was with wifi used sparingly. No 2g or 3g was possible. Slow processor. Crappy screen.
I definitely remember one supposed LCD expert who said Apple was lying about the iPad battery life. Said there was no way it would last more than 3 hours.
I remember a ton of doubt, after launch, that it would be successful, but those people weren't really experts.