You don't get charged anything to use Google Maps with your GPS, so long as you have unlimited data. If you pay-per-use on data then whatever data Gmaps downloads you will be charged for that. But there isn't an additional charge for GPS.
..so gmaps/trapster DO use the GPS even if you haven't paid for the GPS service from your carrier? Your site just links to some apps.
Thought that's what you were looking for....
Those apps use the GPS part of your phone, but that does not cost you anything. GPS only costs you something if you use an app that makes you pay for the app or in the case of AT&T a monthly fee for their turn by turn app.
GPS is a signal you receive, and that signal is free to use. AT&T and other carriers often want you to buy software that uses this GPS signal. You can use other, free software that uses this signal as well.