Aastra 9000i Series Administrator's Manual page 248

.
Aastra Web UI
Step Action
For Global configuration, click on Advanced Settings->Global SIP->Advanced SIP Settings.
1 Or for per-line configuration, click on Advanced Settings->Line N.
2 Enable the "Explicit MWI Subscription" field by checking the check box.
(Disable this field by unchecking the check box. Default is disabled).
If the IP phone has a message waiting subscription with the Service Provider, a Message Waiting
Indicator (MWI) (LED or display icon) tells the user there is a message on the IP Phone.
3 If you enable the "Explicit MWI Subscription" field, then in the "Explicit MWI Subscription Period"
field, enter the requested duration, in seconds, before the MWI subscription times out. The phone
re-subscribes to MWI before the subscription period ends. Default is 86400.
41-001343-01 Rev 02, Release 3.2.2 4-85