Yealink SIP-T40P User Manual page 161

(Enter the primary account 4603 in the Register Name field.)
Click on Advanced, and then select Shared Call Appearance from the pull-down list of
2.
Shared Line.
Enter the desired number in the Number of line key field.
3.
This field appears only if Auto Linekeys is enabled.
The default value is 1. In this example, the value is set to 2.
Advanced Phone Features
149