Yealink SIP-T19 - Manual (Page 108)

User Guide for the SIP-T19P/SIP-T19 IP Phone
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3. Enter the period time in the MWI Subscription Period (Seconds) field.
4. Click Confirm to accept the change.
The IP phone will subscribe to the account number for MWI service by default.
To enable Subscribe MWI to Voice Mail via web user interface:
1. Click on Account->Advanced.
2. Select Enabled from the pull-down list of Subscribe MWI To Voice Mail.
3. Enter the desired voice mail number in the Voice Mail field.
4. Click Confirm to accept the change.