A method of monitoring terminal devices (3, 5, 7), the terminal devices (3, 5, 7) being communicatively connected to a switch device, the method comprising: sending a first message from a first computer device to the switch device after a first communication link is established between the first computer device and the switch device, the first message being configured to start an application session; sending a second message from the switch device to the first computer device in response to the first message; sending a third message from the first computer device to the switch device after receipt of the second message, the third message requesting an identification of all terminal devices (3, 5, 7) of users connected to the switch device that is to be monitored by the first computer device; sending a fourth message from the switch device to the first computer device in response to the third message, the fourth message being configured as a single message that identifies a list of all the terminal devices (3, 5, 7) that the first computer device is to monitor; sending a single monitor start message from the first computer device to the switch device in response to the fourth message to initiate device monitoring for all the terminal devices (3, 5, 7) identified in the fourth message; wherein the identification of the terminal devices (3, 5, 7) to be monitored in the single monitor start message is via the list of the terminal devices (3, 5, 7) that the switch device provides to the first computer device; and activating device monitoring for all of the terminal devices (3, 5, 7) identified in the fourth message at the switch device in response to the single monitor start message such that call control events involving any of the terminal devices (3, 5, 7) that are included in the list of all the terminal devices (3, 5, 7) to be monitored by the first computer device are communicated by the switch device to the first computer device after an acknowledgment of the single monitor start message is sent to the first computer device. sending a first message from a first computer device to the switch device after a first communication link is established between the first computer device and the switch device, the first message being configured to start an application session; sending a second message from the switch device to the first computer device in response to the first message; sending a third message from the first computer device to the switch device after receipt of the second message, the third message requesting an identification of all terminal devices (3, 5, 7) of users connected to the switch device that is to be monitored by the first computer device; sending a fourth message from the switch device to the first computer device in response to the third message, the fourth message being configured as a single message that identifies a list of all the terminal devices (3, 5, 7) that the first computer device is to monitor; sending a single monitor start message from the first computer device to the switch device in response to the fourth message to initiate device monitoring for all the terminal devices (3, 5, 7) identified in the fourth message; wherein the identification of the terminal devices (3, 5, 7) to be monitored in the single monitor start message is via the list of the terminal devices (3, 5, 7) that the switch device provides to the first computer device; and activating device monitoring for all of the terminal devices (3, 5, 7) identified in the fourth message at the switch device in response to the single monitor start message such that call control events involving any of the terminal devices (3, 5, 7) that are included in the list of all the terminal devices (3, 5, 7) to be monitored by the first computer device are communicated by the switch device to the first computer device after an acknowledgment of the single monitor start message is sent to the first computer device.