Telephone headsets connect to a telephone system. A telephone headset functions by replacing the of a telephone. Headsets for standard corded telephones are fitted with a standard commonly called an RJ-9 connector. Headsets are also available with 2.5 mm jack sockets for many DECT phones and other applications. Cordless headsets are available, and often used with . Headsets are widely used for telephone-intensive jobs, in particular by workers. They are also used by anyone wishing to hold telephone conversations with both hands free.
For older models of telephones, the headset microphone is different from that of the original handset, requiring a telephone amplifier for the telephone headset. A telephone amplifier provides basic pin-alignment similar to a telephone headset adaptor, but it also offers sound for the microphone as well as the loudspeakers. Most models of telephone amplifiers offer volume control for loudspeaker as well as microphone, mute function and switching between headset and handset. Telephone amplifiers are powered by batteries or .