A feature that notifies you of new or unheard voicemail messages. This feature is available as a lamp on your phone, a special tone, or as an icon on an online user portal.
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A message-waiting indicator (MWI) in telephony, 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.