I intalled the new Mapquest Navigator on my Curve 8130 and it works quite well. However I too was concerned about running into an area that had no data signal so I called Mapquest support and inquired about this. I was told that when mapquest downloads the map information for your route that it is stored on the BB and you do not need to access the network unless you venture off the routed "Corridore", upon which the app. will try to download more info.
Other than aMaze GPS (Using Turn by Turn only) this is the only Navigation app I know of that retains routing info on the device.
Hope this gives some insight that not all hope is lost.
Correction: I think I am partly dyslexic, I have an 8310 not 8130.