The TAPI LINE_CALLSTATE message is sent when the status of the specified call has changed. Typically, several such messages are received during the lifetime of a call. Applications are notified of new incoming calls with this message; the new call is in the offering state. The application can use lineGetCallStatus to retrieve more detailed information about the current status of the call.




A handle to the call.


The callback instance supplied when opening the call's line.


The new call state. This parameter must be one and only one of the following LINECALLSTATE_ constants.

dwParam1 Meaning
dwParam2 contains details about the busy mode. This parameter uses one of the LINEBUSYMODE_ constants.
dwParam2 contains details about the connected mode. This parameter uses one of the LINECONNECTEDMODE_ constants.
dwParam2 contains details about the dial tone mode. This parameter uses one of the LINEDIALTONEMODE_ constants.
dwParam2 contains details about the connected mode. This parameter uses one of the LINEOFFERINGMODE_ constants.
dwParam2 contains the details about the special information mode. This parameter uses one of the LINESPECIALINFO_ constants.
dwParam2 contains details about the disconnect mode. This parameter uses one of the LINEDISCONNECTMODE_ constants.


Call-state-dependent information. See dwParam1.


In circumstances where a delayed response is appropriate, use LINEDISCONNECTMODE_TEMPFAILURE. Where a blocklisted response is appropriate, use LINEDISCONNECT_BLOCKED. For further information, see LINEDISCONNECTMODE_ Constants.

If dwParam1 is LINECALLSTATE_CONFERENCED, dwParam2 contains the hConfCall parameter of the parent call of the conference of which the subject hCall is a member. If the call specified in dwParam2 was not previously considered by the application to be a parent conference call (hConfCall, the application must do so as a result of this message. If the application does not have a handle to the parent call of the conference (because it has previously called lineDeallocateCall on that handle) dwParam2 is set to NULL.


If zero, this parameter indicates that there has been no change in the application's privilege for the call.

If nonzero, it specifies the application's privilege for the call. This occurs in the following situations: (1) The first time that the application is given a handle to this call; (2) When the application is the target of a call handoff (even if the application already was an owner of the call). This parameter uses one of the following LINECALLPRIVILEGE_ constants.

Return value

No return value.


This message is sent to any application that has a handle for the call. The LINE_CALLSTATE message also notifies applications that monitor calls on a line about the existence and state of outbound calls established by other applications or manually by the user (for example, on an attached phone device). The call state of such calls reflects the actual state of the call, which is not offering. By examining the call state, the application can determine whether the call is an inbound call that needs to be answered or not.

A LINE_CALLSTATE message with an unknown call state can be sent to a monitoring application as the result of a successful lineMakeCall, lineForward, lineUnpark, lineSetupTransfer, linePickup, lineSetupConference, or linePrepareAddToConference that has been requested by another application. At the same time that the requesting application is sent a LINE_REPLY (success) for the requested operation, any monitoring applications on the line are sent the LINE_CALLSTATE (unknown) message. A LINE_CALLSTATE message indicating the "real" call state of the newly generated call is sent (using information provided by the service provider) to the requesting and monitoring applications shortly thereafter.

A LINE_CALLSTATE (unknown) message is sent to monitoring applications only if lineCompleteTransfer causes calls to be resolved into a three-way conference.

For backward compatibility, older applications are not expecting any particular value in dwParam2 of a LINECALLSTATE_CONFERENCED message. TAPI therefore passes the parent call hConfCall in dwParam2 regardless of the API version of the application receiving the message. In the case of a conference call initiated by the service provider, the older application is not aware that the parent call has become a conference call unless it happens to spontaneously examine other information (for example, call lineGetConfRelatedCalls).

This message cannot be disabled.


Requirement Value
TAPI version
Requires TAPI 2.0 or later

See also