We've heard of cell phone concepts that use repetitive motion. The eco-friendly phones designed by ModeLabs use actions inherent in using the phone, like ligting it up, to power the battery. Atlas uses a more retro approach via a wind-up spring.
The exact description from Yanko Design: "It's all made of aluminum and glass...Power comes from kinetic energy similar to that found in watches that use oscillating weight to power a mainspring."
Apparently the phone is closer to old watches than to modern day cellphones as it does not have room for the usual multi-media functions.
When the watch cellphone stops, just give it a shake.