Message Waiting Indicator - MWI
A feature that informs a user that they have messages waiting in email, voice mail, or video mail. Optionally it may indicate how many mail messages are waiting without the user having to call their voice mailbox. MWI may use unique tone (rapidly changing dial time) or an indication on the telephone device (such as a light) as an indication of message waiting. MWI should not impact a subscriber's ability to originate calls or to receive calls. If the dial tone is altered to indicate a message is waiting, it will typically reset to a standard dialtone after a time period or after the user has re-established the connection. As a result, MWI may affect auto-dialers (such as modems) that sense for a dialtone signal before sending the dialed digits. Message waiting indication is also called message waiting notification (MWN)