The best solution is to save the serial number in the resource description.
From the Personal File side menu, select Resources, and then click the ‘Create new resource’ button.
Select the Resource List tab. In the Resource name field, enter the phone model your employees use and click the ‘Add’ button.
Return to the Resources item in the Personal File menu and select the ‘Assign resource’ button.
In the new window, select the employee’s name and phone name from the drop-down list. Enter the serial number of the telephone used by the employee into the description field, and then confirm the new description with the ‘Add’ button. Repeat for all employees who use the same phone model.