Twirling Battery Provides Instant Energy for a Dead Cellphone (inhabitat.com)

Cute, but twirling is not really the best way to harvest energy from a human. Even if your goal is a really really small generator.

It would probably be more effective to twirl the phone too. Easier, less space taken by the ring. You just need a system that makes sure you won't drop the phone by mistake.

Somehow this leads me to imagine pull-cord powered phones.