diff --git a/drivers/isimodem/debug.c b/drivers/isimodem/debug.c
index abdc8a0d..0feea829 100644
--- a/drivers/isimodem/debug.c
+++ b/drivers/isimodem/debug.c
@@ -60,6 +60,10 @@ const char *ss_message_id_name(enum ss_message_id value)
 		_(SS_SERVICE_REQ);
 		_(SS_SERVICE_COMPLETED_RESP);
 		_(SS_SERVICE_FAILED_RESP);
+		_(SS_GSM_USSD_SEND_REQ);
+		_(SS_GSM_USSD_SEND_RESP);
+		_(SS_GSM_USSD_RECEIVE_IND);
+		_(SS_STATUS_IND);
 		_(SS_COMMON_MESSAGE);
 	}
 	return "SS_<UNKNOWN>";
@@ -79,6 +83,7 @@ const char *ss_subblock_name(enum ss_subblock value)
 		_(SS_GSM_INDICATE_PASSWORD_ERROR);
 		_(SS_GSM_INDICATE_ERROR);
 		_(SS_GSM_ADDITIONAL_INFO);
+		_(SS_GSM_USSD_STRING);
 	}
 	return "SS_<UNKNOWN>";
 }
diff --git a/drivers/isimodem/ss.h b/drivers/isimodem/ss.h
index 5118125b..7c20bcce 100644
--- a/drivers/isimodem/ss.h
+++ b/drivers/isimodem/ss.h
@@ -24,16 +24,35 @@
 #ifndef __ISIMODEM_SS_H
 #define __ISIMODEM_SS_H
 
-#define PN_SS		0x06
-#define SS_TIMEOUT	15
+#define PN_SS			0x06
+#define SS_TIMEOUT		15
+#define SS_MAX_USSD_LENGTH	160
 
 enum ss_message_id {
 	SS_SERVICE_REQ = 0x00,
 	SS_SERVICE_COMPLETED_RESP = 0x01,
 	SS_SERVICE_FAILED_RESP = 0x02,
+	SS_GSM_USSD_SEND_REQ = 0x04,
+	SS_GSM_USSD_SEND_RESP = 0x05,
+	SS_GSM_USSD_RECEIVE_IND = 0x06,
+	SS_STATUS_IND = 0x09,
 	SS_COMMON_MESSAGE = 0xF0
 };
 
+enum ss_ussd_type {
+	SS_GSM_USSD_MT_REPLY = 0x01,
+	SS_GSM_USSD_COMMAND = 0x02,
+	SS_GSM_USSD_REQUEST = 0x03,
+	SS_GSM_USSD_NOTIFY = 0x04,
+	SS_GSM_USSD_END = 0x05
+};
+
+enum ss_ussd_status {
+	SS_GSM_STATUS_REQUEST_USSD_START = 0x02,
+	SS_GSM_STATUS_REQUEST_USSD_STOP = 0x03,
+	SS_GSM_STATUS_REQUEST_USSD_FAILED = 0x04
+};
+
 enum ss_operations {
 	SS_ACTIVATION = 0x01,
 	SS_DEACTIVATION = 0x02,
@@ -92,7 +111,8 @@ enum ss_subblock {
 	SS_GSM_PASSWORD_INFO = 0x0B,
 	SS_GSM_INDICATE_PASSWORD_ERROR = 0x0D,
 	SS_GSM_INDICATE_ERROR = 0x0E,
-	SS_GSM_ADDITIONAL_INFO = 0x2F
+	SS_GSM_ADDITIONAL_INFO = 0x2F,
+	SS_GSM_USSD_STRING = 0x32
 };
 
 enum ss_isi_cause {