Drawing Closer: Location Awareness

I'm afraid this is proprietary for the moment, but the idea's clearly generalisable:

Skyhook Wireless Inc....today announced at the 2007 International Consumer Electronics Show (CES) that ReignCom, a Korean manufacturer of media devices, will launch the Wi-Fi enabled iriver W10 portable media player with the Wi-Fi Positioning System from Skyhook Wireless. This device will be the first commercially available media player with location awareness...

The iriver W10 media player is designed for the 'urban explorer.' At a slim 14 mm thick, the iriver W10 comes loaded with full-function multimedia capability. The Wi-Fi Positioning System provides accurate location information by detecting Wi-Fi access points in range and comparing them against a database of geo-located points. Unlike GPS or cell tower systems, the WPS works indoors and in dense urban areas. Not only can a W10 user listen to music, watch movies, or play games on the go, but can also navigate and retrieve information about what is around them.