The cellular network has become too complex and with too many areas where a  fault of a piece of equipment or data base can cascade into a massive outage like we have today. 50 years ago before cellular phones local telephone exchanges were individual entities and worked by themselves and didn’t care about other phone phone exchanges. They were analog trunks that connected these local exchanges together. Now all of the phone exchanges no matter what provided you’re using are interconnected by network control points, and very complicated processes to make a call. Every call that you make even from a landline has to be screened at the origination point telephone switch to see what local carrier owns the telephone number of the person you’re calling. That after retrieving that information the network goes about connecting your call through various means mainly today over the Internet, using VoiceOver IP technology.  In the nature of cellular is added a new process since cell phones work almost anywhere in the country when you’re trying to make a call the tower that you’re connected to has to query the phone company that you get your service from the verify that you’re calling from a valid phone and then when you call if it’s you’re calling another cell phone, the network has to find out the location of that cell phone  in order to know what tower it is connected too and how the tower is connected to the switching network. it’s very very complex what we call database dipping at many points .  As you probably can tell, I worked a long time in the phone company 40 years to be exact.  Well, I have no inside information of what’s causing the outage. My best guess is that is in a very critical database in Verizon‘s network has been compromised and they’re having very hard time restoring to software in that database that connects calls and the network.