If you think about what smartphones are really most like, they're basically pocket-watches: big flat things with a metal case and a glass face that you flip open an optional protective cover to look at, which sit in your pocket when not in use, and trail a cord out of said pocket to somewhere else on your person (your ears, nowadays.)

That said, the word "watch" is likely a very good word to keep for the wrist-devices: their natural UX, given the limited possible set of affordances, is designed around passive alerts. Which is to say, they watch for events, and you watch them.