Index: chan_sip.c
===================================================================
--- chan_sip.c	(revision 207359)
+++ chan_sip.c	(working copy)
@@ -631,6 +631,9 @@
 
 #define SDP_MAX_RTPMAP_CODECS        32               /*!< Maximum number of codecs allowed in received SDP */
 
+#define DEFAULT_CALLBACK             "s"              /*!< Default callback extension when register=yes in peer configuration */
+#define DEFAULT_CALLBACKEXPIRY       "3600"           /*!< Dafault callback expiry when register=yes in peer configuration */
+
 /*! \brief Global jitterbuffer configuration - by default, jb is disabled */
 static struct ast_jb_conf default_jbconf =
 {
@@ -24036,6 +24039,7 @@
 	struct ast_flags peerflags[2] = {{(0)}};
 	struct ast_flags mask[2] = {{(0)}};
 	char callback[256] = "";
+	char callbackexpiry[8] = "";
 	struct sip_peer tmp_peer;
 	const char *srvlookup = NULL;
 	static int deprecation_warning = 1;
@@ -24266,6 +24270,8 @@
 			ast_string_field_set(peer, regexten, v->value);
 		} else if (!strcasecmp(v->name, "callbackextension")) {
 			ast_copy_string(callback, v->value, sizeof(callback));
+		} else if (!strcasecmp(v->name, "callbackexpiry")) {
+			ast_copy_string(callbackexpiry, v->value, sizeof(callbackexpiry));
 		} else if (!strcasecmp(v->name, "callcounter")) {
 			peer->call_limit = ast_true(v->value) ? 999 : 0;
 		} else if (!strcasecmp(v->name, "call-limit")) {
@@ -24526,9 +24532,11 @@
 	peer->the_mark = 0;
 
 	ast_free_ha(oldha);
-	if (!ast_strlen_zero(callback)) { /* build string from peer info */
+	if (!ast_strlen_zero(callback) || !ast_strlen_zero(callbackexpiry)) { /* build string from peer info */
+		if (ast_strlen_zero(callback)) {ast_copy_string(callback, DEFAULT_CALLBACK, sizeof(callback));}
+		if (ast_strlen_zero(callbackexpiry)) {ast_copy_string(callbackexpiry, DEFAULT_CALLBACKEXPIRY, sizeof(callbackexpiry));}
 		char *reg_string;
-		if (asprintf(&reg_string, "%s?%s:%s@%s/%s", peer->name, peer->username, peer->remotesecret ? peer->remotesecret : peer->secret, peer->tohost, callback) < 0) {
+		if (asprintf(&reg_string, "%s?%s:%s@%s/%s~%s", peer->name, peer->username, peer->remotesecret ? peer->remotesecret : peer->secret, peer->tohost, callback, callbackexpiry) < 0) {
 			ast_log(LOG_WARNING, "asprintf() failed: %s\n", strerror(errno));
 		} else	if (reg_string) {
 			sip_register(reg_string, 0); /* XXX TODO: count in registry_count */