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The NPR article[1] gives some more information on what it is. Apparently, it's ultrasonic piezoelectric charging. My guess is that it's using a resonance frequency approach to vibrate the crystals.

1: http://www.npr.org/2011/08/23/139854129/young-entrepreneur-h...

Beamforming would be cool and might actually allow this to work, although I don't know with what efficiency.

That said, the tech just to locate the phones in space to allow the beamforming would be a significant accomplishment itself. But forming the beam or multiple beams to charge multiple devices is probably quite feasible.

A possibly effective option would be sweeping the beam around and having the phone report when it hits. That should be easier than trying to accurately locate the phone first so that you can aim a beam at it.

If you can also make a reasonable initial guess of it's location (to within a few degrees) you could narrow down the guess and check search area considerably.

http://en.wikipedia.org/wiki/Long_Range_Acoustic_Device

http://science.howstuffworks.com/lrad.htm/printable

You can do beamforming with ultrasound. http://www.ted.com/talks/woody_norris_invents_amazing_things The demo device was flat, like the one shown in the article.