[2] Almost all land-line (wired and wireless) telephones have employed sidetone, so it was an expected convention for cellular telephony, but is not standard.
[3][4] One of the benefits of sidetone-enabled phones is that a user knows a call has been dropped or ended if he or she no longer hears sidetone.
Sidetone is disabled when telephones are running in speakerphone mode to prevent direct acoustical feedback from the speaker to the microphone, resulting in howling.
In wireless telegraphy (WT) and amateur radio, sidetone is the audible indication of a continuous wave (CW) signal as the operator sends Morse Code.
When a commentator, announcer, or MC for a public event may otherwise be able to hear their own voice in the delayed output from the loudspeakers, they may opt to use a headset which provides instant sidetone of their own voice, thus removing the distracting effect of greatly delayed auditory feedback from the loudspeakers.