One of the most common household devices in the world today, the telephone is simply a telecommunications device that transmits and receives sound. Usually only two people converse, but, increasingly, today’s phones sport a range of features that have expanded what a phone can do.

Most phones operate through transmission of electrical signals over a complex telephone network. Traditionally, the telephone is referred to as a landline, which means it is hardwired to a telephone line.

Using a landline, a calling party will call a number, and when that phone’s handset is picked up (or the appropriate button is pushed), a button switch or “switch hook” then puts the telephone into an active state by connecting the transmitter (microphone), receiver (speaker), and related audio components to a twisted pair of insulated wires—the telephone line.

Cordless telephones can also be connected to the landline, but these phones have the disadvantage of being inoperable if the base for the phone does not have power.

Cell phones are not connected to a home-wired connection but rather to an independent server.