'это:

Dim objReceivedCallControl As ITBasicCallControl
Set objReceivedCallControl = objCallNotificationEvent.Call

'по идее тоже самое, что это (рекомендую попробовать):

Dim objReceivedCallControl As ITBasicCallControl, objCall as Object
Set objCall = objCallNotificationEvent.Call
Set objReceivedCallControl = objCall 

'а это: 

Dim objReceivedCallControl As ITBasicCallControl, objCall as ITCallInfo 
Set objCall = objCallNotificationEvent.Call
Set objReceivedCallControl = objCall 

'не будет работать никогда

// pEvent is an IDispatch pointer for the ITCallNotificationEvent interface of the
// call object created by TAPI, and is passed into the event handler by TAPI. 

case TE_CALLNOTIFICATION:
{
    // Get the ITCallNotification interface.
    ITCallNotificationEvent * pNotify;
    hr = pEvent->QueryInterface( 
            IID_ITCallNotificationEvent, 
            (void **)&pNotify 
            );
    // If ( hr != S_OK ) process the error here. 
    
    // Get the ITCallInfo interface.
    ITCallInfo * pCallInfo;
    hr = pNotify->get_Call( &pCallInfo);
    // If ( hr != S_OK ) process the error here. 

    // Get the ITBasicCallControl interface.
    ITBasicCallControl * pBasicCall;
    hr = pCallInfo->QueryInterface(
            IID_ITBasicCallControl,
            (void**)&pBasicCall
            );
    // If ( hr != S_OK ) process the error here. 

    // Get the ITAddress interface.
    ITAddress * pAddress;
    hr = pCallInfo->get_Address( &pAddress );
    // If ( hr != S_OK ) process the error here. 

    // Create the required terminals for this call.
    {
        // See the Select a Terminal code example.
    }
    // Complete incoming call processing.
    hr = pBasicCall->Answer();
    // If ( hr != S_OK ) process the error here. 
}