The LINE_CALLSTATE message is sent to an application to notify it about changes in a call's state. The TSPI_lineGetCallInfo function returns mostly constant information about a call as a data structure of type LINECALLINFO. The TSPI_lineGetCallStatus function returns complete call status information for the specified call as a data structure of type LINECALLSTATUS.
The call information data structure maintained for each call contains an application-specific field that applications can read from and write to. This field is not interpreted by the service provider. Applications can use it to tag calls in application-specific ways. Writing to this field so that the change is visible to other applications requires that the application use TSPI_lineSetAppSpecific, which sets the application-specific field of a call's information structure.