[snozolli]

Possibly a Palm Treo, introduced in 2002, or a Windows-based PocketPC, introduced in 2000.

I always felt that Apple basically reimplemented PalmOS with the benefit of ~10 years newer technology and a wildly efficient Chinese supply chain.

I definitely wouldn't say that these devices were mainstream. They were very much targeted toward business people and hardcore nerds. The iPhone definitely revolutionized the market, with its vastly more desirable aesthetic and approachable interface.

[Izkata]

It may have been a 2005 phone or something. I think it was a Nokia, Motorola, or Samsung phone (our whole family was on those at the time), but whatever it was it had just about the complete form factor and an app store - mostly a screen with a grid of apps on home, with a couple of buttons at the bottom (more Android than iPhone). Maybe it had a slide-out keyboard? Can't remember that part for sure.