Do iPhone 5s LTE bands vary from country to country?
There are actually 4 different international variations for the iPhone 5s/5c. Thankfully, Apple has a page outlining them with their model numbers, supported frequencies and countries/carriers you can use them with.

A quick look over that breakdown seems to suggest that Belgium (at least, Mobistar) uses LTE bands 1, 3 or 5, which the US AT&amp;T model also supports. However, I would recommend you contact your carrier to ensure what frequencies are needed to function best on your network.