My wife's computer setup has an old multifunction printer (discontinued Brother MFC-7820N). It includes fax capability, and when we originally bought it, we had an actual telephone landline and the fax worked. We've since moved to another area, where the "landline" is actually VOIP service over Verizon FIOS, and the printer can't even make a connection.
Verizon's online support says that most fax machines should work with it. When I called them to ask about mine not working, their helpful response was that ours must be one of the ones that doesn't.
The printer is from before VOIP, or at least its early days, and its documentation provides no information on compatibility.
There are many online articles about fax with VOIP. The technologies are basically incompatible, but you can sometimes get it to work by using a painfully slow speed setting and turning off error correction (and there's a setting on the printer for that because it's also a solution for some other problems over an actual landline.
Although I did test that, unsuccessfully, the problem occurs even before it starts dealing with the data issues that cause the incompatibility. The printer senses the voltage on the open line, dials the number, and then repeats the handshaking beep. However, I never hear a dial tone over the printer's speaker, or ringing or busy sounds. It just goes through the motions of dialing and beeping until it times out, and then produces a message that the receiving end was either busy or didn't answer.
I'm aware of alternative methods of faxing. My objective here is to figure out why this printer (or any MFP) can't make the initial connection to get a dial tone with VOIP (is there a way to diagnose whether the printer has gone defective, or is this a common problem with VOIP?). If the problem is common to VOIP, is there a fix, or a specification that would identify whether any MFP wouldn't have that problem?