I have found something about in the xda-developers forum (located
HERE).. there is a field test inside the G1, located in Settings > Applications > Manage Applications > Field Test. You can activate in via AnyCut (make a long press in the main screen, then > Shortcut > Any Cut; choose 'Activity' and scroll down to Field Test. Accept it, and run it from Home).
I don't have a G1 yet, but when it comes to me (it will arrive - if there isn't problems - during the next week) I will try this very interesting feature.