Rory Stear: The man behind the crank

The more you wind, the more you charge the phone. An internal battery can also store extra energy, providing the convenience of an extra battery which can be recharged anywhere, anytime.

"This device truly makes the mobile 'mobile' for the very first time," said Mr Stear.

The charger will be available for Motorola phones in March and for most other major mobiles within the year.

It will cost $65, which is out of the reach of many in developing countries. But next year, Freeplay intends to bring out a specific charger for the developing world at half that price.

Cutting the cost

"Sub-Saharan Africa probably only has 20 to 30% electrification - yet the growth of mobile phones has been outstanding," explained Mr Stear.

"Nigeria, for instance, is just opening up and the growth there is incredible."

Trevor Baylis came up with the idea of a clockwork radio

"Some of the service providers in these countries are very interested because it is in their interest to supply access to energy and keep people connected as much as possible."

Mr Stear explained there were even ways of making the charger available at no additional cost to the phone user.

"If the mobile phone providers get involved with the product, I believe there is an opportunity for them to sell a charger along with a phone and a pay-as-you-go contract and obviously subsidise that to consumers," he said.

Freeplay, set up in 1994, is best known for its wind-up radios. It is the world's leading developer of self-sufficient energy technology.