For $24.99 per month, you can get 20MB of data use in the select group of nations while $59.99 will get you 50MB of data use. The overage rate for either plan is $0.005 per kilobyte (or about $5 per megabyte), while data rates in other countries range from $0.010 to $0.0195 per kilobyte.
Though that may sound great to some globe-trotters, remember that the international plans will be in addition to your normal iPhone monthly plan and AT&T's international calling rates. But we're more concerned with how you're supposed to track your usage. Just how are you supposed to know how many kilobytes you're using at a time? Couldn't AT&T have given us a better metric?