Types of Phone Cable
Phone cables come in two standard types and are easy to use once you understand the color coding of the internal wires. It's always wise to have a professional do any wiring, as you can get mildly or severely injured if you do not know what precautions to take before handling electricity.
While phone cables carry low-voltage electricity, they can still harm you if special steps aren't taken when working with them.
Traditional 4-Wire Cable
Homes that were manufactured after 1950 typically have traditional UL approved, twisted pair four-conductor wire. The internal wires are green (transmit 1), red (receive 1), black (transmit 2) and yellow (receive 2). These allow you to wire up to two separate phone lines in your home (with different phone numbers). If you want to replace them, it's easy to use six-conductor wire so that you have an additional two pair if you have problems or want to add a fax or modem.
Cat 5 Cable
All new homes will use the latest Cat 5 cable, which is also four-wire. The color coding is: white (transmit 1), blue (receive 1), white (transmit 2) and orange (receive 2). Cat 5 cable is preferred because it can be used to connect telephones, appliances and even computers all with one cable.
No matter which wire you have in your home, your phone line only needs two of those strands to operate. The other two lines could be used for a different line with a separate phone number, such as for a home office, for example. This makes it handy if you want to install a fax with a dedicated line as well. You can just use the existing two lines which aren't being used. Two-line phones will automatically use the other two wires.