At last month's Consumer Electronics Show in Las Vegas an RCA spokesperson claimed success at charging a BlackBerry from 30% charge to fully charged in around 90 minutes using only ambient WiFi signals as the power source. The gizmo that makes this possible is the RCA Airenergy unit. It converts WiFi signals in free space to dc power to recharge an internal lithium battery. Other devices in need of a charge then plug into the Airenergy battery via a USB port.
The Airenergy battery automatically recharges itself whenever it's anywhere near a WiFi hotspot. Airenergy recharging time depends on the proximity to the WiFi signal and the number of WiFi sources in the vicinity.
Physorg.com carried the story and includes a video of the device shot at CES: