Can you dial and connect to any other telephone number via your Cox-connected phone?
Cox provided Arris device providing dialtone to the house
Not to be a pain, but could you upload an image of this device?
To answer the first question, I've only tried calling a few numbers (local and long distance) and everything went through. The only one getting the disconnected error is the one to the alarm service, and it had been working for over 10 years until April 6.
Here are the pics of the Arris device used for the phone service here. I tried a manual power cycle of it (including removing the battery and letting it sit for 10 minutes), and I tried using the reboot option through the Cox website, but nothing changed.
https://photos.app.goo.gl/HR6LgQYnmCr4hJDv7
https://photos.app.goo.gl/NEVjRaZRj7bpZfGs7https://photos.app.goo.gl/QjtY4CaVDJ3FQLFk9
