Normally mobiles are plugged into chargers, but the new gadget means you don't have to have an electricity supply handy.
The makers of the clockwork charger say this could be useful to people in developing countries, where power supplies are poor.
Motorola will be selling it
The charger, called FreeCharge, gives around five minutes talk time for roughly every minute of winding by hand.
Motorola will be selling the new charger from March, and other companies are expected to follow soon afterwards.