In my earlier iPhone 5 post, I stated that the iPhone now has seperate CDMA and GSM models. I was mistaken. My information came from a Verge article by Dan Seifert, who seems to have been confused as well. Fortunately, the commenters pointed me in the right direction.
Reading the iPhone 5 specs, Apple very clearly states that the CDMA iPhone 5, which is compatible with Verizon and Sprint, is also GSM compatible.
Translation: If you buy a Verizon iPhone, you can use it anywhere in the world.
There are indeed two separate models, but the difference is in the LTE bands. Interestingly enough, the AT&T model uses an LTE band that can only be used in North America, while the Verizon model is fully functional anywhere in the world.
Simply put, Verizon is the way to go if you want an iPhone 5. Sprint if you're on a budget.