In-car GPS vendors are starting to integrate real-time traffic data into their route finding/planning — rather than taking the shortest route, the GSP tries to take traffic into account. In the US, many cities, counties, & states now collect traffic data, and display this data on their own websites. But for GPS companies, hooking into all these various sources is initally expensive, and then continues to be expensive to maintain. And where the city/state/county does not collect this data, there is simply no source of traffic information.
TomTom is trying out an interesting new source of traffic data — partner with a cell phone company (Vodaphone) to get anonymous phone usage statistics. If the phone company sees an unusually large number of cell phones near freeways, that's a good indicator of unusually bad traffic. By partnering with Vodaphone, TomTom can get these anonymous stats from Vodaphone to make better route suggestions. TomTom is calling this service "High Definition Traffic (HD Traffic)".
This is intially a trial in the Netherlands only. If it works well, they will try more Eurpoean countries, and then try to partner with US cell phone companies. If this works, it gives TomTom fewer different sources to integrate with — only once per cell phone company, rather than once per city/county/state. It will also work in areas where the city/county/state does not collect real-time traffic data, or else does not make that data available.