Things You'll Need
Interior phone cable, as needed
Modular telephone jacks are available in single or double configurations and are an easy do-it-yourself project. If you have two telephone lines serving your house, the second jack can be connected to the second phone line, or both jacks can be wired to a single line. The wiring and maintenance of phone lines is the responsibility of the homeowner, and it is not necessary to contact the phone company to make additions or repairs to interior wiring.
Remove the screws holding the existing jack into the wall. If this is a single jack, replace with a dual phone jack. Dual phone jacks are available at most home centers, and you can match them to your existing electrical outlet colors.
Attach the red and green telephone wires to the corresponding terminals on the first jack. Telephone jack terminals are typically marked R (red), G (green), Y (yellow), and B (black). The first jack is now wired for your first phone line. Telephone service only requires two phone wires to be connected, although homes are typically wired with four or more conductors.
Determine if you want the second jack to support your first or second phone line, if available. To connect the second jack to your first phone line, proceed to the next step. If you wish to connect the second jack to a second phone line, skip to step five.
Procure a six-inch piece of interior phone wire, available at most large home centers. Cut the outer insulation lengthwise with a utility knife and peel the insulation away. Remove the red and green conductors from the outer sheath, and strip one inch of insulation from both ends of these wires. Wrap the red wire under the screw labeled "red" on the first jack, and tighten. There should now be two red wires connected to this screw. Repeat with the green wire. Connect the other ends of the new red and green wires to the proper screws on the second jack. The second jack is now connected to your phone line. Skip to step six.
Strip one inch of insulation from the black and yellow conductors. Connect the black wire to the green screw on the second jack and the yellow wire to the red screw on the second jack. The second jack is now wired to your second phone line. Proceed to step six.
Plug a telephone into each jack and verify that it is working correctly.
Mount the phone jack to the wall with the supplied screws.
If you do not have two active phone lines servicing your home, contact your local telephone company. If you are adding a new phone jack, a phone cable can be run from any existing jack to the new location. Connect the new phone wire to the existing circuit by adding wires of the same color to each screw terminal.