iPhone 3G using data on "wi-fi only" in Brazil

[gugy]

I am going to Brazil and I would like to use my iPhone 3G for data only through wi-fi spots while down there.

Is there a way just to do that and completely avoid any AT&T data charges?

Just data, like email, maps, safari, etc, not interested in using the phone feature, since I will carry an old cell and buy a local SIM card.

Thanks for any feedback.