After an application is finished using a line device, it should close the device by calling lineClose on the line-device handle. After the line has been closed, the application's handle for the line device is no longer valid. A LINE_LINEDEVSTATE message is sent to other interested applications to inform them about the state change on the line.
In certain environments, it may be desirable for a line device that is currently open by an application to be forcibly reclaimed (possibly by the use of some control utility) from the application's control. This feature can be used to prevent a single misbehaved application or user from monopolizing a line. It is also used when the user wants to reconfigure the line parameters, and has told the service provider directly through its Setup function in the Telephony Control Panel that the provider should forcibly close the line. When this occurs, an application receives a LINE_CLOSE message for the open line device that was forcibly closed.