As I tweeted excitedly a couple of weeks ago, Augmented Reality is about to make a big splash on our handheld devices. The confluence of video camera, gps and compass in the latest iPhone has made it the platform of the moment, with applications like acrossair—which displays information about New York subway travel—and the less geographically self-limiting (albeit unfortunately named) TwitARound—which displays nearby twitter users and their latest tweets in the virtual field of vision—attracting attention. This isn't mainstream yet, but it's a compelling indication of what's to come.
Holding a phone to one's face is going to become a common exercise, it seems. I can imagine something less bulky like a lanyard or a rectangular monocle (circular, once round LEDs are readily available; tethered or wireless) becoming a popular alternative. Some kind of screen-only video thingie which could be cabled up to a handheld would make a great prototype. Alternatively, anyone know how hard it would be to hack a second LCD screen—with, say, a 1.5m cable—onto a 3GS? :)