I'm on wifi so much I don't notice. Plus, I live in a small town in Oklahoma that doesn't have AT&T LTE. I have a Verizon 8x that I use as a backup phone, and I must say reception and data away from home is so much better on the RM-937. I'm guessing that, despite being unlocked, the Verizon 8x doesn't have the necessary bands for AT&T data.
One thing I noticed, and maybe I just didn't pay attention with my AT&T 1520, is that the included sim tool is slightly different. The sim tray was already slid out slightly, but when I went to pop the memory card door out, I couldn't do it with my old(er) Nokia sim tool. At first I thought the door was broken, but then on a hunch I checked the included sim tool, and it worked with no problem. Putting them side by side showed the 1520 sim tool to be slightly, but importantly, longer: