Using the Service Observing feature, designated users can listen to another user calls.

From AE Services Release 8.1.3 and Communication Manager Release 8.1.3 onwards, a new third-party call control support is added for the activation and deactivation of service observe, service observe connection mode change, query service observe status, and monitor service observe the state change, on a hard phone. Service observer state change events are only sent on station monitors if the ASAI version is 12 or later.