Some customers - those of us who've been with AT&T for a Really Long Time (tm) - actually have an unlimited
international data plan, distinct from unlimited domestic data. It may have only been originally offered to customers associated with certain corporate accounts - not sure. What I do know is I've had mine for years and years and years, and while it's a little pricey (especially in the months when I don't use the roaming feature), the convenience makes it such that I'm probably the only AT&T customer to ever ask for the maximum possible contract length extension every time I upgrade
