I don't like to attach a holder to the windscreen and connect a cable to the 12V socket each time I want to use my navigation.
So I got myself a Brodit Phone Holder with power cable and build it in the Spacestar fixed above the rear view mirror.
Now I only have to stick the Phone into the holder when I want to use the navigation system (Sygic) and pull it out when I'm done. Works Perfectly