Busy Lamp Fields and Shared Line Appearances can be set in the portal for each user who has a desktop phone that supports these features.
A Shared Line Appearance places a line key on your desktop phone that serves as another end-point for calls from that seat. You can hear the ring, answer the calls directly, access voicemail, and even make outbound calls as that line appearance.
A Busy Lamp Field places a line key on your desktop phone that serves as a speed-dial to that seat. It also displays the hook state of the other end (red for off-hook, blinking green for ringing, etc).
Locate the seat in the Locations section of the Customer Administration Portal
Press the EDIT icon on the left to open the Manage Settings window
Select the Call Control tab and scroll down to "Shared Line Appearance/Busy Lamp Field"
You can add new Shared Line Appearances and Busy Lamp Fields with the appropriate buttons
Shared Line Appearances will be prioritized above Busy Lamp Fields.
Only Admins can alter these settings in the Customer Administration Portal
You can add any user seat from your PBX as a BLF, but only user seats in your location as SLA
If the number of SLA/BLF exceed the lines available for your phone, and you do not have an expansion module, they will not provide any functionality