When should "In Service" be announced?

The appropriate time to announce "In Service" is when a unit is ready and available for calls. This status indicates that the unit is prepared to respond to emergencies or duties as needed. Being "In Service" signifies to dispatch and other units that the crew is not only operational but also at a state where they can immediately take calls and engage in necessary actions.

When a unit declares itself "In Service," it effectively communicates its readiness to provide assistance, which is crucial in emergency management and law enforcement. Having units available ensures that they can be dispatched promptly to incidents, thereby enhancing the overall efficiency of the response system.

The context surrounding the other options reveals why they are less suitable. A unit that is not operational, busy with other matters, or dealing with unclear communication cannot be considered "In Service," as these states indicate a lack of availability or readiness to respond to incidents.