Telephone cords are one of the more basic types of cables. Phone cables have remained mostly the same over the years with a few small changes here and there. There is a little terminology to know that will tell you a bit more about your phone lines, such as how they are wired and what type of plastic connector is on the end of the cable.
Phone cords come in two varieties, flat cords used to connect phones to the wall and coiled cords used for handset receivers. Flat cords will use either an RJ11 or RJ12 connector. These two connectors are the same size and look the same on the outside. On the inside, RJ11 will have four metal contacts for the internal wires inside the cable while RJ12 has six contacts. Since they are the same size, RJ12 is backwards compatible with RJ11. However, since RJ11 is the older of the two it is not compatible with RJ12.
The next distinction is whether your flat cord is straight or reverse. Straight cables are used to send data, like a fax machine, while reverse cables are used for voice, like a telephone. On a straight cable, the wires will connect to the same metal pins on either side of the cable. Pin 1 to pin 1, pin 2 to pin 2, etc. On a reverse cable, the opposite is true. For RJ12, a reverse cable would go pin 1 to pin 6, pin 2 to pin 5, etc.
Round versions of the flat cord also exist but are usually used for something other than a phone. Typically, they are equipped with extra features that make them larger than the average flat cable, such as something built for outdoor use or a cable designed to connect an Internet modem to a wall jack.
A straight pinout (left) vs. a reverse pinout (right)
Coiled phones cords are made to connect handset receivers to the base of the phone. The connectors on these are smaller than the ones on a flat line cord, using either an RJ9 or RJ22 connector. RJ9 and RJ22 are two different names for the same thing. Being smaller than RJ11/RJ12, these connectors only have room for four metal contacts instead of six.
The size of a coiled phone cord can be somewhat confusing. Most companies will list the size the cord would be if it was completely uncoiled. On average, 6 feet of uncoiled cord equals about 1 foot coiled. So if you order a phone cord labeled “6 feet” for length, it will be 1 foot coiled up all the way and stretch to about 3-4 feet. Coiled phone cords are generally made in four sizes: 6 feet (1 foot coiled; small), 12 feet (2 feet coiled; medium), 25 feet (4 feet coiled; long), and 50 feet (8 feet coiled; extra-long).
Exactly how far a cord will stretch varies from cable to cable. The strain from extended stretching can potentially break the cable or send your phone crashing to the floor. Long, worn out cords are also get tangled easier but this can be remedied by using a cord detangler.