The Nokia Research Centre in Cambridge is working on creating a mobile phone that draws power from ambient radio waves – WiFi or TV signals, for example – to avoid the need for batteries in a similar way to early ‘crystal set’ radios and today’s RFID tags.
Researchers are currently working to create a prototype that could ‘harvest’ up to 50 milliwatts of power; a ten-fold increase from current designs that can manage 3 to 5 milliwatts. It's only a research project at the moment... but you never know. [Sources: TechnologyReview.com; Nokia Conversations]