MWI = Message Waiting Indicator

Usually an audio or visual signal that a voicemail or other type of message is waiting. Examples:
  • Stutter dial-tone
  • Flashing light on phone
  • Vibration
  • Periodic special ring
  • etc.

IP phones

Most IP phones support a MWI indicator, and most ATA's support stutter dial-tone. Asterisk also supports stutter tone on Zaptel FXS adapters.

The following ATAs can be configured to additionally light an LED on the base unit for MWI:

The following IP phones are known have trouble displaying MWI:
  • Budgetone BT-101/BT-102 claims to, but does not (Wrong: The LCD backlights blicks to indicate MWI)

Analog phones

Some analog phones also support MWI via a 90V neon lamp - requires hardware support on the FXS interface. Supported by:

ISDN phones/devices

Have a look at ETS 300 650 and ETS 300 196 ( To do this stuff with a PC and a standard ISDN controller have a look at
CAPI 2.0 4. edition part 3 "Supplementary Services" (
It would come in an "Information" message with a Feature Activation for the proper button/key number.

See also:

Not to be confused with: MBWA
Created by: jht2, Last modification: Fri 02 of Nov, 2012 (00:20 UTC) by electron
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