Project Turns GPS Phones Into Traffic Reporters
TomTom takes anonymized location information from mobile phone handsets in The Netherlands, and make traffic reports they call HD traffic.
The handsets are not (necessarily) equipped with GPS chips, but their location is triangulated by the GSM network itself. The mobile network (Vodafone NL) supplies the information to TomTom, who then process it into traffic reports.
They claim to cover 10 times more roadarea than conventional traffic detection that uses inductive loops embedded in the roads. (The conventional system is already quite extensive in The Netherlands, which is a small and densely populated country). I seem to recall TomTom also have some sort of patent.