What appears to be erratic behavior with voice mail indicator on a phone may sometimes be the result of an extension belonging to a shared mailbox. In this case, if the shared mailbox is set to alert subscribed users via a message waiting indicator, a user’s MWI lamp may light when the shared mailbox receives a message. If the extension also has an MWI (message waiting indicator) and the message in the shared mailbox is checked by the user the phone may turn off the MWI even though there is still a voicemail in the local user's extension. This is the result of the phone instrument not differentiating between the 2 message caches.
The Strategic Voice Solutions network notifies the phone of a message waiting and also provides information about which account has a message (i.e. number of the shared mailbox or extension number in this case). Most phones, however ignore this extra information and simply turn the lamp on and off, irrespective of the status of the individual accounts.
In order to avoid this situation, it is recommended that either the User or the Shared Mailbox be set to Only email the message rather than send and MWI.