In light of certain $3000 iPhone data bills for international roaming, it's fair to assume that many of us don't really know what the exact policy is jet set iPhone living. The skinny is this, from AT&T directly: "For $24.99 per month, iPhone users get 20MB of data use outside the US. If you don't have a plan, the cost is $.0195/KB. If you are on the plan, the overage charge is $.005/KB." Originally, I was told that the $25 would cover unlimited international data, but it turns out that this only covers the 20MB, so that's the final word.
I think this is somewhat fair, but I'd recommend AT&T give power users a 100 or 150MB plan. Chen and I used ~180MB each in month one. Now stop your bitching about AT&T. We don't mind giving them a hard time when they mess up, but everyone charges for international Data. That's just how it is.