If you are in the US on att and going over there you should just leave data roam setting on the iPhone off!!! They have one plan for iPhone for $20 which gives you like 20MB total of data. BB's on att get a $50 unlimited data plan for worldwide which makes a lot more sense.
You should add the international calling plan for $5.99 to lower the talk time cost and turn it off when you get back (it's prorated $5.99, but make sure all you calls clear before you turn it off). For data just find wifi hot spots.