So their Ericsson appliances/applications have somehow failed.
Perhaps they should have avoided this single point of failure for such a critical piece of comms infrastructure (using redundant bits of kit from the same supplier doesn't work if all instances of it are affected by the same issue).
If other operators around the world are affected then it sounds like a botched update, or a very well coordinated cyberattack. Or perhaps they're all using some cloudy service and THAT has gone down?