Assertion: phone system's line | /r/AtLocation | use
Facets:
value: on a call
type: TEMPORAL
Source sentences:
text: Headset does not designate when other lines are in use, you must use the base station.
text: Lamp steadily lit: The line is in use on a call
text: Important: if you underestimate this, callers will get a busy signal if all the lines are in use.