I think the ## codes are carrier specific. Boost and Virgin Mobile are both technically Sprint so that's why the code works for those carriers. Have you tried updating profile and PRL (both of which should be under Settings > More > System Update), and then restarting your phone? Other than that, a factory reset usually solves problems related to updates like the KitKat one, but you will lose anything you haven't backed up. Also, you could check with an AT&T retailer, or even post on the forum here, to see if anyone has similar codes for your phone. Good luck!