Or you can port the number to google voice, which is free. Then set up an obi box
OBiTALK. Get wireless phones for each room you want a phone in. Done.
If you want 911 on phones get punch alert
911+ | PunchAlert
One time charge for equipment. Free afterwards because you just set up the same VOIP phone system the cable company charges you 30-40 a month for.
Phones calls take very little bandwidth. Been using this setup for over 10 years with no issues. Best part it’s portable, you move it moves with you ..plug and play.
Cable company routers are the best to use with their service. Off the shelf store routers can cause slowness, in my experience.