Use the lineGetCallWaitingState function to retrieve the list of media modes for which call waiting is enabled.
LONG WINAPI lineGetCallWaitingState( HLINE hLine, LPDWORD lpdwClasses );
The line device handle. The line device handle must have been previously obtained by a call to lineOpen with the proper TAPI device ID specified and a device-specific extension version successfully negotiated with lineNegotiateExtVersion. For more information about lineNegotiateExtVersion and lineOpen, see the TAPI Functions API Reference topics on MSDN.
Points to a DWORD indicating which line capability classes are enabled for call waiting. See the Line Capability Classes constants for possible values.
Returns zero if the function completes successfully, or a negative error number if an error occurs. The following are possible return values:
This function is synchronous. No LINE_REPLY message is sent. Not implemented for CDMA.
Pocket PC: Pocket PC 2002 and later.
Smartphone: Smartphone 2002 and later.
OS Versions: Windows CE 3.0 and later.
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