You'll want to double check with your cable modem provide if they allow you to use your own cable modem for phone usage. Since it's not easy to find, I suspect most don't let you since they provide it to you anyways.
In my home it's a silly gigantic all-in-one cable modem/WiFi/voice box/4 port gigabit. When I 1st received it before calling them, I toyed around with it and saw all the options. Most I would have turned off. After calling to have them set it up as a cable modem bridge and voice only. I can no longer login to manage, but it is setup as a cable modem bridge with landline voice. The 4 ports work, but once you plug in one that gains access, the other just light up but don't appear to do much. By the way, it was free, no monthly charge and was at the max channels my cable provider supports so I left it be.