A phone cord is of different PIN types. It varies from 1 pin, 2 pin, 3 pin, 4 pin, 5 pin, 6 pin and many more. This cord or cable will be connected to the phone port or to a wall jack. When the plug is plugged in, the cables are connected to each other physically and the circuit is completed. Each pin gets in contact with the corresponding pin for which they are assigned a task to be performed. This cable is called Registered Jack (RJ cable)
This is how RJ Cable looks like:
In the countries like US, Canada and UK, they will have preinstalled home phone wiring service for using telephones, fax lines. With this wiring system, they can connect the cordless phones to each home wiring port and extend the home phone service.
Read: Vonage Account Login: Use iphone or Android as Cordless Answering Phones
You ay watch the video below to learn about 2 PIN and 4 PIN cable: