I don't know anyone's phone number. They're all entered on my mobile. But if for some reason I don't have it handy, I can look up anyone I need with a phone book or 411.
If the navigation system goes down, can you stop at a gas station and buy a map? Usually. For now. Will they disappear as nav systems become common? Maybe.
I agree that you don't build that mental model, though. There are places that I only go with my wife -- her relatives, the craft store, etc. If she's not there giving me directions, I have no idea where I am.