While that may be technically true for a strict definition of “smartphone,” there’s no denying the iPhone redefined the concept in a way that its competitors were forced to copy to have any hope of keeping up. Nobody hears the word “smartphone” and thinks of a Blueberry or Treo anymore.
That's a subjective question, so I'll give a subjective answer. The browser, for better or worse, was a lot less dumbed down for mobile than competitors, the stylus-less touch interface reduced UI friction and the odds that you'd lose a critical (if inexpensive) component, and the slew of contemporary iPod users could easily migrate their libraries over.
It preceded its release with the iPod craze, making it a lifestyle product rather than something marketed for its capabilities (which were very humble compared to other contemporary devices and only started to catch up in second gen).