The iPhone was an incremental, evolutionary development from the smartphones of 2006
Did you actually use any smartphones in 2006?
The typical smartphone of 2006 - think BlackBerry Curve or Motorola Q - was a keyboard-driven (it may or may not have had a touchscreen, and if it did it probably had a stylus) and optimized to do e-mail and calendaring passably well. The experience of browsing the web on BB OS or Windows Mobile (or, God help you, Windows CE) was so painful as to be something you did in a pinch because you had to, not because you wanted to. Built-in apps were generally carrier-loaded crapware. Don't even get me started on how difficult it was to do things like, you know, make phone calls.
So the smartphone of 2006 was basically a decent mobile e-mail device, and that's it. The all-touchscreen, web-friendly user experience of the iPhone - remember, back then stuff like "pinch to zoom" was a big deal that nobody had seen before - was radically different. It may have been evolutionary, but it certainly wasn't incremental.