The application layer of a UA should be able to specify the SIP response code (404, 486, etc.) to send back to the caller when rejecting a call. But neither interface for doing so (sipxCallReject and CallManager::rejectConnection) provides this capabillity. (sipxCallReject has arguments for this purpose, but they are ignored.)

The call-reject request is bucket-brigaded through this sequence of operations:

sipXcallReject
CallManager::rejectConnection
CP_REJECT_CONNECTION message to CallManager
CP_REJECT_CONNECTION message to CpCall
CpPeerCall::handleRejectConnection
SipConnection::reject

But SipConnection::reject determines the response code to use based entirely on the current state of the call; the application can provide no information.