Rotary telephones are not compatible with Xfinity Voice service.
But in https://forums.xfinity.com/t5/Home-Phone-Features/Pulse-Dialing-Is-It-a-Possibility/m-p/3217253#M509... employee @ComcastJoeTru stated that it might be possible.
This fixes your phone to dial out. It's the easiest little box to hook up, plug and works right away. Plug into the back of your modem where the phone line plugs in and works for the WHOLE house. Took less than 3 seconds to hook up. Costs $40 plus $14 shipping from Australia. its AWESOME!