Use the Busy Indicator feature to provide multiappearance telephone users and attendants with a visual indicator of the busy or the idle status of one of the following system resources:
An extension number
A trunk group
A terminating extension group (TEG)
A hunt group, either direct department calling (DDC) or uniform call distribution (UCD)
Any loudspeaker paging zone, including all zones
Note:
A SIP phone can only support another extension.