--- chan_sip.c.orig	2008-08-27 12:27:52.000000000 +0200
+++ chan_sip.c	2008-08-27 18:01:55.000000000 +0200
@@ -988,11 +988,12 @@
 #define SIP_PAGE2_BUGGY_MWI		(1 << 26)	/*!< DP: Buggy CISCO MWI fix */
 #define SIP_PAGE2_REGISTERTRYING        (1 << 29)       /*!< DP: Send 100 Trying on REGISTER attempts */
 #define SIP_PAGE2_UDPTL_DESTINATION     (1 << 30)       /*!< DP: Use source IP of RTP as destination if NAT is enabled */
+#define SIP_PAGE2_Q850_REASON           (1 << 31)       /*!< DP: Get/send cause code via Reason header */
 
 #define SIP_PAGE2_FLAGS_TO_COPY \
 	(SIP_PAGE2_ALLOWSUBSCRIBE | SIP_PAGE2_ALLOWOVERLAP | SIP_PAGE2_VIDEOSUPPORT | \
 	SIP_PAGE2_T38SUPPORT | SIP_PAGE2_RFC2833_COMPENSATE | SIP_PAGE2_BUGGY_MWI | \
-	SIP_PAGE2_TEXTSUPPORT | SIP_PAGE2_UDPTL_DESTINATION)
+	SIP_PAGE2_TEXTSUPPORT | SIP_PAGE2_UDPTL_DESTINATION | SIP_PAGE2_Q850_REASON)
 
 /*@}*/ 
 
@@ -7570,12 +7571,24 @@
 	add_header_contentLength(&resp, 0);
 	/* If we are cancelling an incoming invite for some reason, add information
 		about the reason why we are doing this in clear text */
-	if (p->method == SIP_INVITE && msg[0] != '1' && p->owner && p->owner->hangupcause) {
-		char buf[10];
-
-		add_header(&resp, "X-Asterisk-HangupCause", ast_cause2str(p->owner->hangupcause));
-		snprintf(buf, sizeof(buf), "%d", p->owner->hangupcause);
-		add_header(&resp, "X-Asterisk-HangupCauseCode", buf);
+	if (p->method == SIP_INVITE && msg[0] != '1' && p->owner) {
+			char buf[10];
+			char buf2[20];
+
+		if(p->owner->hangupcause) {
+			if(ast_test_flag(&p->flags[1], SIP_PAGE2_Q850_REASON)) {
+				sprintf(buf2, "Q.850;cause=%i", p->owner->hangupcause);
+				add_header(&resp, "Reason", buf2);
+			}
+			add_header(&resp, "X-Asterisk-HangupCause", ast_cause2str(p->owner->hangupcause));
+			snprintf(buf, sizeof(buf), "%d", p->owner->hangupcause);
+			add_header(&resp, "X-Asterisk-HangupCauseCode", buf);
+		} else if(ast_test_flag(&p->flags[1], SIP_PAGE2_Q850_REASON)) {
+			strncpy(buf, msg, 3);
+			buf[4] = '\0';
+			sprintf(buf2, "Q.850;cause=%i", hangup_sip2cause(atoi(buf)));
+			add_header(&resp, "Reason", buf2);
+		}
 	}
 	return send_response(p, &resp, reliable, seqno);
 }
@@ -12748,6 +12761,7 @@
 		ast_cli(fd, "  Sess-Refresh : %s\n", strefresher2str(peer->stimer.st_ref));
 		ast_cli(fd, "  Sess-Expires : %d secs\n", peer->stimer.st_max_se);
 		ast_cli(fd, "  Min-Sess     : %d secs\n", peer->stimer.st_min_se);
+		ast_cli(fd, "  Use Reason   : %s\n", ast_test_flag(&peer->flags[1], SIP_PAGE2_Q850_REASON) ? "Yes" : "No");
 		ast_cli(fd, "\n");
 		unref_peer(peer);
 	} else  if (peer && type == 1) { /* manager listing */
@@ -12830,7 +12844,7 @@
  				astman_append(s, " %s,%s\r\n", v->name, v->value);
 			}
 		}
-
+		astman_append(s, "SIP-Use-Reason-Header : %s\n", (ast_test_flag(&peer->flags[1], SIP_PAGE2_Q850_REASON))?"Y":"N");
 		unref_peer(peer);
 
 	} else {
@@ -15272,6 +15286,7 @@
 	char *c_copy = ast_strdupa(c);
 	/* Skip the Cseq and its subsequent spaces */
 	const char *msg = ast_skip_blanks(ast_skip_nonblanks(c_copy));
+	char *rp = NULL;
 
 	if (!msg)
 		msg = "";
@@ -15279,9 +15294,16 @@
 	sipmethod = find_sip_method(msg);
 
 	owner = p->owner;
-	if (owner) 
-		owner->hangupcause = hangup_sip2cause(resp);
-
+	if (owner) {
+		if (ast_test_flag(&p->flags[1], SIP_PAGE2_Q850_REASON) && (rp = strstr(get_header(req, "Reason"), "cause="))) {
+			rp += 6;
+			owner->hangupcause = atoi(rp);
+			if (req->debug)
+				ast_verbose("Using Reason header for cause code:%i\n", owner->hangupcause);
+		} else {
+			owner->hangupcause = hangup_sip2cause(resp);
+		}	
+	}
 	/* Acknowledge whatever it is destined for */
 	if ((resp >= 100) && (resp <= 199))
 		__sip_semi_ack(p, seqno, 0, sipmethod);
@@ -20578,6 +20600,8 @@
 			} else {
 				peer->stimer.st_ref = i;
 			}
+		} else if (!strcasecmp(v->name, "use_q850_reason")) {
+			ast_set2_flag(&peer->flags[1], ast_true(v->value), SIP_PAGE2_Q850_REASON);
 		}
 	}