Yealink SIP-T42G User Manual page 157

To configure the auto linekeys feature via web user interface:
Click on Features->General Information.
1.
Select Enabled from the pull-down list of Auto LineKeys.
2.
Auto LineKeys is
If
for a registered shared line on the phone.
Click Confirm to accept the change.
3.
you can automatically assign multiple DSS keys with Line type
enabled,
Advanced Phone Features
143