Google Maps API allows us to develop applications that use data retrieved from google servers such as street views, routes, satellite views, traffic data and others.
You can use this data within apps you develop for various platforms including platforms for mobile telephones.
Recently, google has released the Google Maps Navigation app for the android platform. The following video clip presents this app.
More info about Google Maps API can be found at
More info about the Google Maps Navigation app for mobile telephones can be found at http://www.google.com/mobile/navigation/