Message-waiting indicator

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In telephony, a message-waiting indicator (MWI) is a Telcordia Technologies (formerly Bellcore) term for an FSK-based telephone calling feature that illuminates an LED on selected telephones to notify a telephone user of waiting voicemail messages on most North American public telephone networks and PBXs.

As described in Telcordia Generic Requirements document GR-283-CORE, a Message_Waiting_Indicator (MWI) is a mechanism that informs the subscriber about the status of recorded messages.^{[verification needed]} The subscriber may subscribe to a notification feature that makes use of the status of this MWI.