Our telephone provider, Callcentric, reported a DoS attack, which I thought was the reason we lost dial tone for several days. The service has been working fine for months.
However, Callcentric said the issues were solved yesterday, and we still could not connect. I was ready to create a support ticket with the company, but then I went on a search through the house wiring. I found the underlying issue appears to be a hungry bunny in our house with excellent timing, as detailed in this picture of the phone cord under the kitchen desk.