Tokyo University has developed a touchless interface that can register 3D motion of a human finger using a single camera. Think of it like Project Natal, only with mobile phones.
The camera requires video capture at 154fps - so the handful of mobile phones out there with forward-facing cameras will not be able to handle the technology. However, it is certainly plausible down the line. The question is, will anyone want it? I mean, fingerprint smudging is a pain in the arse and everything, but I don't want to be the guy walking down the street wildly flailing my fingers in the air like some sort of lunatic. Plus, it seems like it would be difficult to use in general. [Gigazine via Intomobile via Geek]