http://www.navigadget.com/index.php/2008/03/30/...
As you may already know the first two way internet connected Dash Express comes with a service plan (optional). This connectivity is mostly via cellular networks, and Dash’s partner for providing this server is Jasper Wireless. Jasper is an aggregator and can provide coverage over a variety of networks. Now it is important to understand you’ll still be able to navigate anywhere even if the whole network is down - because the maps are stored on the device and GPS signals come from outer space, not Jasper.
http://www.navigadget.com/index.php/2008/03/30/dash-coverage-map/trackback/