The iPhone 5 comes in three different models. Confusing, eh? 4G LTE bands are so dispersed that a world phone is no longer possible when it comes to fast 4G data connections. So, Apple has 3 models of the iPhone 5 to help cover its bases. But which model is the right choice for you? Here are a few articles to disambiguate the situation:
Mashable: iPhone 5: All the New Stuff
And from Apple: iPhone 5 models, LTE bands, and countries they are deployed in.