--- ./asterisk-1.8.0/channels/chan_sip.c	2010-10-15 22:12:04.000000000 +0200
+++ ./asterisk-1.8.0-szabolcs/channels/chan_sip.c	2010-11-05 11:22:28.000000000 +0100
@@ -6360,7 +6360,20 @@
 		break;
 	case AST_CONTROL_CONGESTION:
 		if (ast->_state != AST_STATE_UP) {
-			transmit_response_reliable(p, "503 Service Unavailable", &p->initreq);
+			switch (ast->hangupcause){
+			    case AST_CAUSE_UNREGISTERED:
+				transmit_response_reliable(p, "480 Temporarily unavailable", &p->initreq);
+				break;
+			    case AST_CAUSE_NO_ANSWER:
+				transmit_response_reliable(p, "480 Temporarily unavailable", &p->initreq);
+				break;
+			    case AST_CAUSE_NORMAL_UNSPECIFIED:
+				transmit_response_reliable(p, "480 Temporarily unavailable", &p->initreq);
+				break;
+			    default:
+				transmit_response_reliable(p, "503 Service Unavailable", &p->initreq);
+				break;
+			}
 			p->invitestate = INV_COMPLETED;
 			sip_alreadygone(p);
 			ast_softhangup_nolock(ast, AST_SOFTHANGUP_DEV);