I don't know the "Nav launcher". It looks like the Tattoo comes with different apps in different countries. We have Google Maps. And although you can get a position fix only with the GPS active (i.e. without WiFi or data connection) you would not have much use of it without a map. And you can only access Google Maps with some kind of connection to the internet (e.g. WiFi or Data).
To EddersC: If you start Google Maps and shut i down again. Then turning of Wifi and data and starting Google Maps again. The Tattoo will have remembered the previous accessed map. Trouble comes to you when you are on the move now, thus requiring new maps... Then you will begin to miss you data-connection
