In this old Wired magazine article from January 2008, Fred Vogelstein—who had what seems to be unrivaled access to insider information from unnamed Apple (and AT&T?) employees in researching his piece—jotted down what seemed at the time to be a relatively insignificant detail (emphasis mine):
[In February 2005] Jobs delivered a three-part message to Cingular: Apple had the technology to build something truly revolutionary, “light-years ahead of anything else.” Apple was prepared to consider an exclusive arrangement to get that deal done. But Apple was also prepared to buy wireless minutes wholesale and become a de facto carrier itself.
Jobs had reason to be confident. Apple’s hardware engineers had spent about a year working on touchscreen technology for a tablet PC and had convinced him that they could build a similar interface for a phone.
Again, Vogelstein had an unprecedented level of access to details of the top secret project, so there’s no reason to treat this as conjecture.
Now, was that “tablet PC” envisioned as the iPad that we have today? No, of course not. But it does show that Apple was planning on exploring touch-screen portable computers well before they took that technology to make a phone with it.
Don’t make the mistake of thinking that Apple sees the iPad as anything other than their most significant product on the market today.