Q:

Do iPhone 5s LTE bands vary from country to country?

From this article,

The 5s and the 5c are compatible with more 4G LTE frequency bands — up to 13, instead of a maximum five before. That means the phone is more likely to work with higher speeds wherever you go. However, there are more than 40 cellular bands worldwide, the bulk for LTE, so a version bought in one country might not work for high speeds everywhere around the world.

Say one were to buy an iPhone 5s in the United States and take it to Europe (specifically, Belgium). Would there be any performance impact, given the purported differences in cellular bands?

A:

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&T model also supports. However, I would recommend you contact your carrier to ensure what frequencies are needed to function best on your network.

