Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 126511)
+++ channels/chan_sip.c	(working copy)
@@ -3924,7 +3924,7 @@
 		break;
 	case AST_CONTROL_BUSY:
 		if (ast->_state != AST_STATE_UP) {
-			transmit_response(p, "486 Busy Here", &p->initreq);
+			transmit_response_reliable(p, "486 Busy Here", &p->initreq);
 			p->invitestate = INV_COMPLETED;
 			sip_alreadygone(p);
 			ast_softhangup_nolock(ast, AST_SOFTHANGUP_DEV);
@@ -3934,7 +3934,7 @@
 		break;
 	case AST_CONTROL_CONGESTION:
 		if (ast->_state != AST_STATE_UP) {
-			transmit_response(p, "503 Service Unavailable", &p->initreq);
+			transmit_response_reliable(p, "503 Service Unavailable", &p->initreq);
 			p->invitestate = INV_COMPLETED;
 			sip_alreadygone(p);
 			ast_softhangup_nolock(ast, AST_SOFTHANGUP_DEV);