diff -Naru asterisk_orig/channels/chan_sip.c asterisk/channels/chan_sip.c
--- asterisk_orig/channels/chan_sip.c	2011-07-28 12:56:15.000000000 +0200
+++ asterisk/channels/chan_sip.c	2011-07-28 13:05:37.000000000 +0200
@@ -8701,6 +8701,8 @@
 	/* SRTP */
 	int secure_audio = FALSE;
 	int secure_video = FALSE;
+	int clear_audio_offered = FALSE;
+	int clear_video_offered = FALSE;
 
 	/* Others */
 	int sendonly = -1;
@@ -8824,6 +8826,9 @@
 			} else if (strcmp(protocol, "AVP")) {
 				ast_log(LOG_WARNING, "unknown SDP media protocol in offer: %s\n", protocol);
 				continue;
+			} else {
+				/* We have been offered plain audio */
+				clear_audio_offered = TRUE;
 			}
 			audio = TRUE;
 			p->offered_media[SDP_AUDIO].offered = TRUE;
@@ -8852,6 +8857,9 @@
 			} else if (strcmp(protocol, "AVP")) {
 				ast_log(LOG_WARNING, "unknown SDP media protocol in offer: %s\n", protocol);
 				continue;
+			} else {
+				/* We have been offered plain video */
+				clear_video_offered = TRUE;
 			}
 			video = TRUE;
 			p->novideo = FALSE;
@@ -9014,8 +9022,12 @@
 
 	if (secure_audio && !(p->srtp && (ast_test_flag(p->srtp, SRTP_CRYPTO_OFFER_OK)))) {
 		ast_log(LOG_WARNING, "Can't provide secure audio requested in SDP offer\n");
-		res = -4;
-		goto process_sdp_cleanup;
+		if ( clear_video_offered ) {
+			ast_log(LOG_WARNING, "Falling back to offered unsecure audio\n");
+		} else {
+			res = -4;
+			goto process_sdp_cleanup;
+		}
 	}
 
 	if (!secure_audio && p->srtp) {
@@ -9026,8 +9038,12 @@
 
 	if (secure_video && !(p->vsrtp && (ast_test_flag(p->vsrtp, SRTP_CRYPTO_OFFER_OK)))) {
 		ast_log(LOG_WARNING, "Can't provide secure video requested in SDP offer\n");
-		res = -4;
-		goto process_sdp_cleanup;
+		if ( clear_video_offered ) {
+			ast_log(LOG_WARNING, "Falling back to offered unsecure video\n");
+		} else {
+			res = -4;
+			goto process_sdp_cleanup;
+		}
 	}
 
 	if (!p->novideo && !secure_video && p->vsrtp) {