Ear and mouth (E&M) is a technology in voice over IP (VoIP) that uses a traditional telephone handset with an earphone (or earpiece) for listening to incoming audio and a microphone (or mouthpiece) for transmitting audio. Calls using an E&M interface can be made from, received from, or disconnected by a private branch exchange (PBX) as well as from a VoIP-capable computer.
The main advantage of E&M is the fact that it allows a PBX to reliably detect disconnect (hang-up) signals. This eliminates problems that can otherwise occur with locked computer ports at the terminations of calls, and thus minimizes the risk of needlessly consuming network resources.
The term ear and mouth interface is sometimes used as a synonym for a telephone handset itself, or for a headset-and-microphone combination that allows hands-free operation.