Originally Posted by tangfish

Because it's a % and not a data amount, then for instance receiving even a single iMessage while overseas, in the absence of usage in the US in that billing cycle, would count as a strike. You get two strikes and on the third, you're out. This is not a big deal to people who travel for a week here and there, but for someone who spends some number of months outside the US per year, it can be a tricky game of tapdance to play with billing cycles and such.