Busy Lamp Fields are used as indicators to show the status of a person's phone line. The BLF will only display for people within your organization and does not apply to external lines.

Business Voice

Polycom VVX

The BLF will appear as an icon depicting a user or phone on your phone and expansion module. A registered line will show as a phone icon, while a monitored line within the business group will show up as a user icon. Monitored line icons will update in real time as they are in use. 

Phone line is not registered
Phone line is registered.
Shared phone line is registered.
Phone line is registered and is idle.
Phone line is registered and is in use.