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3gs is fitted with a GPS chip, it doesn't need a data connection it needs a clear view of the sky like any GPS device
If it doesn't have a data connection it will take a whole lot longer to gain a fix if it's location has changed, up to 15 minutes. Nothing to do with the iPhone, a general GPS thing.
I don't use TT, i have MotionX GPS and it gives me options in the set up to use
a) Outdoor GPS Mode
b) WiFi or Network Triangulation
c) Manual Mode.
Might be worth checking/changing youirs if you have no luck