When I use Ovi maps and there is no wifi or data connection the search will not return any streets or cities when I want to plan a route. I've installed complete europe with the map loader and I can navigate all over the maps but finding a destination with the search is simply not possible.

For example if I search for amsterdam it returns nothing found. When i activate the wifi it finds the smallest street in amsterdam.

Is there an option to get the navigation working without an internet connection and retrieve the desired adress in offline mode.

I don't think the N900 have support for searching inside the maps for streets. I know that the symbian version can do that, but it's way better to use online search, it finds businesses and other things that is not embedded in the maps. Maybe they'll add this in the next update?

Yes but if you live near the border or spend lots of time in another country than you're constant on a roaming network and that means everytime a new destination is entered in the navigation it costs money.