I don't have the NAV so when I need directions, I look at Google Maps.
Not sure if you are aware, but Google Maps recently (okay, it may have been a few months ago) added a very neat feature.
As you may know, Google Maps allows you to get directions between any two points.
But what if you don't like the directions?
What if you want to make a detour?
You can now drag the route line and drop it anywhere you want and it will instantly recalculate the mileage, drive time (which is always incorrect and, most importantly, turn by turn instructions).
Here is a link to take you from Beverly Hills to New York.
Hover anywhere on the blue line and you will see a white circle.
Find a point along the line to 'pull' and drag the line and drop it on a city. Make sure you see the tool tip pop up that says "Drag to change route" or you will be dragging the map instead of the line.
It is a very cool feature!

(not sure if other mapping services have this, or not)

 

Another great feature Google Maps for Smartphones. Google Maps provides live traffic updates and can give you turn by turn directions through your phone. Cost - Absolutely free.

http://mobile.google.com

 

Mobile internet usage charges?

 

I would assume the normal Internet usage charges. It does show the amount of data transferred, but our phones are setup with the Internet package.

 

Some smart phones allow you to use a dial up networking (DUN) connection. This uses your minutes. That said, it is also much slower.

 

Don't know about your area but Google Maps also allows me to plot a route and then get bus route directions instead of driving directions.

Also those of you with TomToms can now send stuff from Google Maps to your TomTom. Just browse for a business name (e.g. a restaurant or a shop). Click SEND, click GPS and then it'll load up your HOME program. From there you can choose to "Navigate There" or "Save as Favourite" or "View Map"