Phones are not working

The Friday before Christmas our 3 phones all stopped working at the same time. Our DSL, however, was unaffected, which I thought was rather odd. After several calls to SBC and following their instructions to unplug all our phones (to somehow "reset" the system) and then after checking to make sure none of the phones themselves were defective, I requested a service call. Someone came out to the house to check outside wiring, which they said was OK. I wasn't home, but Mom said the repair person asked if they could check inside, and when they did, the phones worked again. Mystery. No clue as to what happened.
I say all this because our phones have all stopped working again. What you get is a busy signal if you try and call. Call the cell phones if you need to get in touch.