--- chan_pjsip.c	2016-07-07 13:41:14.042564655 +0200
+++ chan_pjsip_modified.c	2016-07-07 13:44:07.418564655 +0200
@@ -1690,25 +1690,83 @@
 	ast_channel_queue_connected_line_update(session->channel, &connected, NULL);
 }
 
+/*!
+ * \brief Set a custom SIP header
+ *
+ * This sets a custom header and adds it to an outgoing SIP request. If the header already exists on the message,
+ * then no action is taken.
+ *
+ * \pre chan is locked.
+ *
+ * \param header_name The name of the SIP header to add to the outgoing message.
+ * \param tdata The outgoing SIP message on which to add the header
+ */
+static void add_header_custom(const char *header_name, const char *header_value, pjsip_tx_data *tdata)
+{
+        pj_str_t pj_header_name;
+        pjsip_hdr *header;
+
+        pj_cstr(&pj_header_name, header_name);
+        header = pjsip_msg_find_hdr_by_name(tdata->msg, &pj_header_name, NULL);
+        if (header) {
+                return;
+        }
+        ast_sip_add_header(tdata, header_name, header_value);
+}
+
 static int call(void *data)
 {
-	struct ast_sip_channel_pvt *channel = data;
-	struct ast_sip_session *session = channel->session;
-	struct chan_pjsip_pvt *pvt = channel->pvt;
-	pjsip_tx_data *tdata;
-
-	int res = ast_sip_session_create_invite(session, &tdata);
-
-	if (res) {
-		ast_set_hangupsource(session->channel, ast_channel_name(session->channel), 0);
-		ast_queue_hangup(session->channel);
-	} else {
-		set_channel_on_rtp_instance(pvt, ast_channel_uniqueid(session->channel));
-		update_initial_connected_line(session);
-		ast_sip_session_send_request(session, tdata);
-	}
-	ao2_ref(channel, -1);
-	return res;
+        struct ast_sip_channel_pvt *channel = data;
+        struct ast_sip_session *session = channel->session;
+        struct chan_pjsip_pvt *pvt = channel->pvt;
+        pjsip_tx_data *tdata;
+
+        struct varshead *headp;
+        struct ast_var_t *current;
+
+        int res = ast_sip_session_create_invite(session, &tdata);
+
+        if (res) {
+                ast_set_hangupsource(session->channel, ast_channel_name(session->channel), 0);
+                ast_queue_hangup(session->channel);
+        } else {
+                //Check if there are any variables that need to be set before initiating the call
+                ast_channel_lock(session->channel);
+
+                headp = ast_channel_varshead(session->channel);
+                AST_LIST_TRAVERSE(headp, current, entries) {
+                        /* PJSIPADDHEADER: Add SIP header to outgoing call */
+                        if (!strncmp(ast_var_name(current), "PJSIPADDHEADER", strlen("PJSIPADDHEADER"))) {
+                                char *content, *end;
+                                const char *header = ast_var_value(current);
+                                char *headdup = ast_strdupa(header);
+                                /* Strip off the starting " (if it's there) */
+                                if (*headdup == '"') {
+                                        headdup++;
+                                }
+                                if ((content = strchr(headdup, ':'))) {
+                                        *content++ = '\0';
+                                        content = ast_skip_blanks(content); /* Skip white space */
+                                        /* Strip the ending " (if it's there) */
+                                        end = content + strlen(content) -1;
+                                        if (*end == '"') {
+                                                *end = '\0';
+                                        }
+                                        add_header_custom(headdup, content, tdata);
+                                        ast_debug(1, "Adding SIP Header \"%s\" with content %s \n", headdup, content);
+                                }
+                        }
+                }
+
+                ast_channel_unlock(session->channel);
+
+
+                set_channel_on_rtp_instance(pvt, ast_channel_uniqueid(session->channel));
+                update_initial_connected_line(session);
+                ast_sip_session_send_request(session, tdata);
+        }
+        ao2_ref(channel, -1);
+        return res;
 }
 
 /*! \brief Function called by core to actually start calling a remote party */