Before you get too excited, let's start with the disclaimers. For starters, while yes, some users over on XDA managed to get LTE service working in very select AT&T markets, this probably won't work in your area. Also, this is not the intended use of your phone, so if you're not comfortable screwing with radios on your phone, you should probably skip the whole freaking out thing.
So, here's how it goes. The Nexus 4 technically "doesn't" have support for LTE in that it does support certain bands due to the default hardware present in the Optimus G that this handset is built off of, but it lacks the capability to utilize most major bands (there are 25 separate LTE bands). If you're on AT&T and you're using LTE, chances are you're connected via band 17, which operates on the 700 MHz frequency.