I hope the wrist device has some sort of overworld motion, like lighting up when you get a call. Actually, I'm not just hoping for it. I expect it. If they don't make it so, I'd say they didn't take full advantage of the advanced graphics. It's a small thing, but sometimes it's the small things that add to the feel.
Also, with the absence of a screen, it seems highly probable that the display is holographic.
Edit: I've just noticed this, and I have no idea if it's already been mentioned (or if it's even worthy of note), but:
Of course, the device is on the official character art, but for something to be present in the earlier trailer but not in the more recent one seems a little backwards to me.