Message Waiting And Call Status Indicator (Mwi) - Nortel Meridian M3900 Reference Manual

Table 8
Key numbers
Key number
Key 1
Key 2
Key 3
Key 4
Keys 5-16
Key 17
Key 18
Key 19
Key 20
Key 21
Key 22
Key 23
Key 24
Key 25
Key 26-27
Key 28
Key 29
Key 30-32
Note: Keys 18-25 and 28-29 are the keys labeled as the four context-sensitive softkeys.

Message Waiting and Call Status Indicator (MWI)

The MWI LED lights to show a message is waiting. This indicator
visually alerts that a call is holding. The LED flashes to indicate an
incoming call. It winks when a call is holding.
Meridian SL-100 M3900 Meridian Digital Telephones Reference Guide
Location
Labeled as Prime DN (shown as 5000).
Labeled as second Line/Feature (shown as 5001).
Labeled as Prime DN, accessed by using the Shift key (shown as
5000).
Labeled as second Line/Feature, accessed by using the Shift key
(shown as 5001).
Blocked.
Key labeled as Message.
Transfer (CXR).
Six-party Conference (CNFC06).
Call Forward (CFU).
Ring Again (RAG).
Call Park (CPK).
Call Pick-up (CPU).
Speed Call Short (SCS), Long (SCL), or User (SCU).
Privacy release (PRL).
Null.
Callers List.
Redial List.
Null.
M3903 enhanced telephone 45