So I got a brand new Iphone 3G from an independent seller (purchased from an ATT store) and inserted my SIM that has absolutely no data plan associated with it and the phone works fine obviously without constant internet access. Now my issue is: Everything that I've read online says that it will work but that ATT will charge you up the wazoo for using any online services when not connected to wifi but my experience is that the features that use internet connection (web-browser, Email, Voice Mail push, etc,) don't work at all and I get a pop-up message saying that it won't work without a data plan. So does that mean I'm in the clear as far as possible hidden charges from using it as a my cell phone?

What about GPS? When I have wifi turned off the GPS service still seems to work but it's very choppy, as if it's getting info from surrounding wifi signals rather than from the cell towers. My wife has the same phone only with the data plan and her GPS works smoothly. Am I being charged when using the GPS maps feature? I KNOW it's not connected to the internet because the search feature doesn't work (and actually tells me that I am not connected) but the GPS feature continues to function?!?