For me it works automatically in Wifi mode... once you've got your account in Navizon, enter your details on the main screen. From then on it briefly shows you that login screen and starts finding you.
For me it finds my position in wifi mode within about 5 seconds and it's amazing how close it is...within about 20 meters but you need to be able to see other routers for it to work - install NetStumbler to see what your iphone can see...
I'm in a urban area so there's at least 4-6 routers active here.
~Kooga