diff --git a/src/libmsc/gsm_09_11.c b/src/libmsc/gsm_09_11.c
new file mode 100644
index 0000000..8f7e54f
--- /dev/null
+++ b/src/libmsc/gsm_09_11.c
@@ -0,0 +1,159 @@
+/* (C) 2008-2009 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2008, 2009 by Holger Hans Peter Freyther <zecke@selfish.org>
+ * (C) 2009 by Mike Haben <michael.haben@btinternet.com>
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+/**
+ * MSC-specific handling of call independent Supplementary
+ * Services messages (NC_SS) according to GSM TS 09.11
+ * "Signalling interworking for supplementary services".
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+
+#include <osmocom/msc/gsm_04_80.h>
+#include <osmocom/msc/gsm_subscriber.h>
+#include <osmocom/msc/debug.h>
+#include <osmocom/msc/osmo_msc.h>
+#include <osmocom/msc/vlr.h>
+#include <osmocom/msc/gsm_04_08.h>
+#include <osmocom/msc/transaction.h>
+
+/* FIXME: choose a proper range */
+static uint32_t new_callref = 0x20000001;
+
+/* Declarations of USSD strings to be recognised */
+const char USSD_TEXT_OWN_NUMBER[] = "*#100#";
+
+/* A network-specific handler function */
+static int send_own_number(struct gsm_subscriber_connection *conn,
+			   const struct ss_request *req)
+{
+	char *own_number = conn->vsub->msisdn;
+	char response_string[GSM_EXTENSION_LENGTH + 20];
+
+	DEBUGP(DMM, "%s: MSISDN = %s\n", vlr_subscr_name(conn->vsub),
+	       own_number);
+
+	/* Need trailing CR as EOT character */
+	snprintf(response_string, sizeof(response_string), "Your extension is %s\r", own_number);
+	return gsm0480_send_ussd_response(conn, response_string, req);
+}
+
+/* Entry point for call independent MO SS messages */
+int gsm0911_rcv_nc_ss(struct gsm_subscriber_connection *conn, struct msgb *msg)
+{
+	struct gsm48_hdr *gh = msgb_l3(msg);
+	struct gsm_trans *trans;
+	struct ss_request req;
+	uint8_t pdisc, tid;
+	uint8_t msg_type;
+	int rc;
+
+	pdisc = gsm48_hdr_pdisc(gh);
+	msg_type = gsm48_hdr_msg_type(gh);
+	tid = gsm48_hdr_trans_id_flip_ti(gh);
+
+	/* Associate logging messages with this subscriber */
+	log_set_context(LOG_CTX_VLR_SUBSCR, conn->vsub);
+
+	DEBUGP(DMM, "Received SS/USSD data (trans_id=%x, msg_type=%s)\n",
+		tid, gsm48_pdisc_msgtype_name(pdisc, msg_type));
+
+	/* Reuse existing transaction, or create a new one */
+	trans = trans_find_by_id(conn, pdisc, tid);
+	if (!trans) {
+		/**
+		 * According to GSM TS 04.80, section 2.4.2 "Register
+		 * (mobile station to network direction)", the REGISTER
+		 * message is sent by the mobile station to the network
+		 * to assign a new transaction identifier for call independent
+		 * supplementary service control and to request or acknowledge
+		 * a supplementary service.
+		 */
+		if (msg_type != GSM0480_MTYPE_REGISTER) {
+			LOGP(DMM, LOGL_ERROR, "Unexpected message (msg_type=%s), "
+				"transaction is not allocated yet\n",
+				gsm48_pdisc_msgtype_name(pdisc, msg_type));
+			gsm0480_send_ussd_reject(conn, &req,
+				GSM_0480_PROBLEM_CODE_TAG_GENERAL,
+				GSM_0480_GEN_PROB_CODE_UNRECOGNISED);
+			return -EINVAL;
+		}
+
+		DEBUGP(DMM, " -> (new transaction)\n");
+		trans = trans_alloc(conn->network, conn->vsub,
+			pdisc, tid, new_callref++);
+		if (!trans) {
+			DEBUGP(DMM, " -> No memory for trans\n");
+			gsm0480_send_ussd_return_error(conn, &req,
+				GSM0480_ERR_CODE_SYSTEM_FAILURE);
+			return -ENOMEM;
+		}
+
+		trans->conn = msc_subscr_conn_get(conn, MSC_CONN_USE_TRANS_NC_SS);
+		trans->dlci = OMSC_LINKID_CB(msg);
+		cm_service_request_concludes(conn, msg);
+	}
+
+	memset(&req, 0, sizeof(req));
+	rc = gsm0480_decode_ss_request(gh, msgb_l3len(msg), &req);
+	if (!rc) {
+		LOGP(DMM, LOGL_ERROR, "SS/USSD message parsing error, "
+			"rejecting request...\n");
+		gsm0480_send_ussd_reject(conn, &req, GSM_0480_PROBLEM_CODE_TAG_GENERAL,
+			GSM_0480_GEN_PROB_CODE_UNRECOGNISED);
+		/* The GSM 04.80 API uses inverted codes (0 means error) */
+		return -EPROTO;
+	}
+
+	/* Interrogation or releaseComplete? */
+	if (req.ussd_text[0] == '\0' || req.ussd_text[0] == 0xFF) {
+		if (req.ss_code > 0) {
+			/* Assume interrogateSS or modification of it and reject */
+			return gsm0480_send_ussd_return_error(conn, &req,
+				GSM0480_ERR_CODE_ILLEGAL_SS_OPERATION);
+		}
+		/* Still assuming a Release-Complete and returning */
+		return 0;
+	}
+
+	msc_subscr_conn_communicating(conn);
+	if (!strcmp(USSD_TEXT_OWN_NUMBER, (const char *)req.ussd_text)) {
+		DEBUGP(DMM, "USSD: Own number requested\n");
+		rc = send_own_number(conn, &req);
+	} else {
+		DEBUGP(DMM, "Unhandled USSD %s\n", req.ussd_text);
+		rc = gsm0480_send_ussd_return_error(conn, &req,
+			GSM0480_ERR_CODE_UNEXPECTED_DATA_VALUE);
+	}
+
+	/**
+	 * TODO: as we only handle *#100# for now, and always
+	 * respond with RELEASE COMPLETE, let's manually free
+	 * the transaction here, until the external interface
+	 * is implemented.
+	 */
+	trans_free(trans);
+
+	return rc;
+}