How to Connect a Comcast Phone Box

Comcast offers phone service over the Internet.

Comcast Digital Voice uses Voice over Internet Protocol (VoIP) technology to power its calls. The phone box provided is actually a modem (eMTA) specifically designed to handle this technology. Internet service, however, will not be available unless you have signed up for it specifically. When you first establish phone service, a Comcast technician installs your phone box to your cable and your phone. Re-connecting the phone box takes no special tools and just a few minutes of your time.

Connecting Without Internet

Step 1

Unplug your phone box (modem) from the power. You can usually do this from the back of the box itself, or by unplugging the cord from the electrical outlet.

Step 2

The cable line (coaxial cable) designated for your phone service or Internet is the only one that will work correctly. The cable is usually black with a silver end piece. On the back of your phone box, locate the connection labeled "Cable." It will have threads and a small hole in the center. Align the pin on the inside of the silver piece of the cable as well as the threads, and screw the cable to connect it to the phone box. Secure with your fingers without overtightening.

Step 3

Plug the line from your home telephone into the back of your phone box. If you have only one phone line, use the slot labeled "Telephone 1" only. Align the tabs and press until you hear a click.

Step 4

Plug the phone box back into the power. It can take a couple of minutes for the box to communicate and establish a connection. You might see your phone lights, as well as the lights on the modem, flashing. Once they have stabilized, test your phone for a dial tone.

Connecting With Internet Service

Step 1

Customers with Internet service as well must unplug their phone box, as well as their computer and/or router. Continue as indicated above by connecting your cable line and connecting your phone line.

Step 2

Connect the Ethernet cable line connected to your computer or router into the back of the phone modem in the "Ethernet" slot. The Ethernet line looks similar to a phone line, but is noticeably larger.

Step 3

When powering on your phone box and computer, you will first plug in the phone box/modem. Allow the lights to stabilize and a dial tone to be established. If using a router, power it on next. Once the modem and/or router lights have stopped scanning (one or two will flash randomly), power on your computer for an Internet connection.

Things You'll Need

  • Comcast eMTA modem

  • Comcast Digital Voice service


Only authorized Comcast technicians can install new Comcast Digital Voice service.


If you are uncertain about making the right connections, contact Comcast for additional technical support at 800-266-2278.