A computer error message that always makes my heart skip a beat. The problem is either something silly, perhaps from tripping over the phone cord earlier or leaving the phone off the hook. Or it is something really nasty, as in something that only a trained professional can fix. These trained professionals are strictly rationed by the phone company in such a way that you may find yourself without phone service for a couple of days, maybe more if the problem happens on a Thursday or Friday.
The last time it happened to me I was without service for 5 days, from a Thursday evening to the following Tuesday afternoon. Of course, I had to take off work to be at home to meet the repairman. Turns out the problem was caused by a squirrel or some other small mammal chewing on wires in the neighborhood switch box.