Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 206094)
+++ channels/chan_sip.c	(working copy)
@@ -12637,7 +12637,6 @@
 	case 183:	/* Session progress */
 		if (!ast_test_flag(req, SIP_PKT_IGNORE) && (p->invitestate != INV_CANCELLED) && sip_cancel_destroy(p))
 			ast_log(LOG_WARNING, "Unable to cancel SIP destruction.  Expect bad things.\n");
-		/* Ignore 183 Session progress without SDP */
 		if (find_sdp(req)) {
 			if (p->invitestate != INV_CANCELLED)
 				p->invitestate = INV_EARLY_MEDIA;
@@ -12646,6 +12645,18 @@
 				/* Queue a progress frame */
 				ast_queue_control(p->owner, AST_CONTROL_PROGRESS);
 			}
+		} else {
+			/* Alcatel PBXs are known to send 183s with no SDP after sending
+			 * a 100 Trying response. We're just going to treat this sort of thing
+			 * the same as we would treat a 180 Ringing
+			 */
+			/*XXX I'm just following the same procedure for a 180 response, which
+			 * doesn't change the invitestate of p. Shouldn't it be INV_PROCEEDING
+			 * though?
+			 */
+			if (!ast_test_flag(req, SIP_PKT_IGNORE) && p->owner) {
+				ast_queue_control(p->owner, AST_CONTROL_RINGING);
+			}
 		}
 		check_pendings(p);
 		break;