Are the Google Maps Navigation Android phones with turn by turn navigation (Google Maps Navigation), are the maps preinstalled?

In December 2010 (after Jacob's answer) a new version of Google Maps for Android was released: this now uses intelligent caching to download and cache map data for the areas you travel in most: as well as using new dynamic-drawing technology that means maps use up "100-times less data". These maps are downloaded automatically when you are plugged in to power, and using wifi (i.e. your nightly charge). This also means that re-routing now works much better offline. (It does still use some data, by the way: notably for traffic information and more map detail. You could always try turning your phone into airplane mode if this concerns you.) http://googleblog.blogspot.com/2010/12/next-generation-of-mobile-maps.html

No - the map "tiles" are downloaded from the Internet on-demand like they are with the standard Google Maps application. You will incur data charges as a result. The Navigation app does do some intelligent stuff around caching your route in case you happen to lose your data connectivity while driving. But this seems pretty hit-or-miss. We were led wildly off-course in rural Vermont once when the voice prompts stopped. I think when it's operating in "offline" mode, it gets confused the second you wander off-route. Update: Maps has changed significantly since I wrote this. See 's answer for a more up to date description.