telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunications services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is ...

, a message-waiting indicator (MWI) is a

Telcordia Technologies iconectiv supplies communications providers with network planning and management services. The company’s cloud-based information as a service network and operations management and numbering solutions span trusted communications, digital identi ...

(formerly

Bellcore iconectiv supplies communications providers with network planning and management services. The company’s cloud-based information as a service network and operations management and numbering solutions span trusted communications, digital identi ...

) term for an FSK-based

telephone A telephone, colloquially referred to as a phone, is a telecommunications device that enables two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most ...

calling feature that illuminates an

LED A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresp ...

on selected

telephones A telephone, colloquially referred to as a phone, is a telecommunications device that enables two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most ...

to notify a telephone user of waiting

voicemail A voicemail system (also known as voice message or voice bank) is a computer-based system that allows callers to leave a recorded message when the recipient has been unable (or unwilling) to answer the phone. Calls may be directed to voicemail m ...

messages on most North American public telephone networks and PBXs. As described in Telcordia Generic Requirements documen
GR-283-CORE
a Message_Waiting_Indicator (MWI) is a mechanism that informs the subscriber about the status of recorded messages. The subscriber may subscribe to a notification feature that makes use of the status of this MWI.

Difference to audible message waiting indicators

This feature is also frequently called (and abbreviated) as visual message waiting indicator (VMWI). A VMWI, as defined i
Telcordia GR-1401-CORE
is a stored program controlled switching (SPCS) system feature that activates and deactivates a visual indicator on

customer-premises equipment In telecommunications, a customer-premises equipment or customer-provided equipment (CPE) is any terminal and associated equipment located at a subscriber's premises and connected with a carrier's telecommunication circuit at the demarcation p ...

(CPE) to notify the customer that new messages are waiting. VMWI differs from existing features that use other message indicators, such as audible stuttered

dial tone A dial tone (dialling tone in the UK) is a telephony signal sent by a telephone exchange or private branch exchange (PBX) to a terminating device, such as a telephone, when an off-hook condition is detected. It indicates that the exchange is ...

, in that it activates a visual indicator on the CPE. The visual indicator may be as simple as lighting or flashing a

light-emitting diode A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corre ...

(LED), or as advanced as displaying a special message on a

liquid-crystal display A liquid-crystal display (LCD) is a flat-panel display or other Electro-optic modulator, electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers to display information. Liq ...

(LCD). This technology was invented by Jerome (Jerry) Schull and Wayne Howe at BellSouth's Advanced Technology R&D group in 1992 and was issued as US Patent
#5,363,431
and

It was introduced in 1995, with the introduction of CLASS-based calling features and ADSI. It was at one time only compatible with ADSI-compliant telephones but is now compatible with any customer premises equipment ( CPE) that simply responds visually to visual FSK.

Use of similar indicator on standalone Caller ID set-top boxes

This service is often erroneously associated with the abilities of most

Caller ID Caller identification (Caller ID) is a telephone service, available in analog and digital telephone systems, including voice over IP (VoIP), that transmits a caller's telephone number to the called party's telephone equipment when the call is ...

standalone set-top boxes. Caller ID boxes manufactured after 1998 feature an

that blinks green to notify that new calls have been recorded and red to indicate that a subscriber has new voicemail messages waiting. Some units also display the text "MESSAGE WAITING" (similar to ADSI-compliant telephones). These units do not use visual FSK to activate their red LEDs, but instead, they briefly " pick-up" the line at certain intervals (normally, within two minutes of a new call) to check for a "stuttered"

. The presence of a stutter dial tone activates a red LED; while absence deactivates it.

Mobile telephony

For

mobile phone A mobile phone or cell phone is a portable telephone that allows users to make and receive calls over a radio frequency link while moving within a designated telephone service area, unlike fixed-location phones ( landline phones). This rad ...

s, the message-waiting indicator is sent via a

Short Message Service Short Message Service, commonly abbreviated as SMS, is a text messaging service component of most telephone, Internet and mobile device systems. It uses standardized communication protocols that let mobile phones exchange short text messages, ...

(SMS) message — the same system used for

texting Text messaging, or texting, is the act of composing and sending electronic messages, typically consisting of alphabetic and numeric characters, between two or more users of mobile phones, tablet computers, smartwatches, desktops/laptops, or ...

. (SMS was actually invented for utilitarian uses like this, not for user conversation.) It not only indicates that a message is waiting, but also how many unheard messages there are on the voicemail

server Server may refer to: Computing *Server (computing), a computer program or a device that provides requested information for other programs or devices, called clients. Role * Waiting staff, those who work at a restaurant or a bar attending custome ...

for that

telephone number A telephone number is the address of a Telecommunications, telecommunication endpoint, such as a telephone, in a telephone network, such as the public switched telephone network (PSTN). A telephone number typically consists of a Number, sequ ...

. In the event that a phone is deactivated, out of range, or otherwise removed from the network, there is often no way to clear this indicator until another message is recorded to the system, causing the MWI message to be sent again once the phone reconnects. The

customer service Customer service is the assistance and advice provided by a company to those who buy or use its products or services, either in person or remotely. Customer service is often practiced in a way that reflects the strategies and values of a firm, and ...

call center A call centre (English in the Commonwealth of Nations, Commonwealth spelling) or call center (American English, American spelling; American and British English spelling differences#-re, -er, see spelling differences) is a managed capability th ...

for the

mobile network operator A mobile network operator (MNO), also known as a mobile network provider, mobile network carrier, mobile , wireless service provider, wireless carrier, wireless operator, wireless telco, or cellular company, is a telecommunications provider of se ...

may also be able to provide simple

technical support Technical support, commonly shortened as tech support, is a customer service provided to customers to resolve issues, commonly with consumer electronics. This is commonly provided via call centers, online chat and email. Many companies provid ...

to reset this by resending the MWI message manually.

Difference to audible message waiting indicators

Use of similar indicator on standalone Caller ID set-top boxes

Mobile telephony

See also