Yealink SIP-T42S User Manual page 193

Select Enabled from the pull-down list of Subscribe for MWI.
3.
Enter the period time in the MWI Subscription Period(Seconds) field.
4.
Click Confirm to accept the change.
5.
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:
Click on Account->Advanced.
1.
Select the desired account from the pull-down list of Account.
2.
Select Enabled from the pull-down list of Subscribe for MWI.
3.
Select Enabled from the pull-down list of Subscribe MWI To Voice Mail.
4.
Advanced Phone Features
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