--- a/dom/system/gonk/ril_consts.js
+++ b/dom/system/gonk/ril_consts.js
@@ -897,23 +897,23 @@ const PDU_PID_ANSI_136_R_DATA           
 const PDU_PID_ME_DATA_DOWNLOAD             = 0x7D;
 const PDU_PID_ME_DEPERSONALIZATION         = 0x7E;
 const PDU_PID_USIM_DATA_DOWNLOAD           = 0x7F;
 
 // DCS - Data Coding Scheme
 const PDU_DCS_MSG_CODING_7BITS_ALPHABET  = 0x00;
 const PDU_DCS_MSG_CODING_8BITS_ALPHABET  = 0x04;
 const PDU_DCS_MSG_CODING_16BITS_ALPHABET = 0x08;
-const PDU_DCS_MSG_CLASS_ME_SPECIFIC      = 0xF1;
-const PDU_DCS_MSG_CLASS_SIM_SPECIFIC     = 0xF2;
-const PDU_DCS_MSG_CLASS_TE_SPECIFIC      = 0xF3;
+const PDU_DCS_MSG_CLASS_UNKNOWN          = 0xFF;
+const PDU_DCS_MSG_CLASS_0                = 0x00;
+const PDU_DCS_MSG_CLASS_ME_SPECIFIC      = 0x01;
+const PDU_DCS_MSG_CLASS_SIM_SPECIFIC     = 0x02;
+const PDU_DCS_MSG_CLASS_TE_SPECIFIC      = 0x03;
 const PDU_DCS_CODING_GROUP_BITS          = 0xF0;
-const PDU_DCS_CODING_GROUP_7BITS_DISCARD = 0xC0;
-const PDU_DCS_CODING_GROUP_7BITS_STORE   = 0xD0;
-const PDU_DCS_CODING_GROUP_16BITS_STORE  = 0xE0;
+const PDU_DCS_MSG_CLASS_BITS             = 0x03;
 const PDU_DCS_MWI_ACTIVE_BITS            = 0x08;
 const PDU_DCS_MWI_ACTIVE_VALUE           = 0x08;
 const PDU_DCS_MWI_TYPE_BITS              = 0x03;
 const PDU_DCS_MWI_TYPE_VOICEMAIL         = 0x00;
 const PDU_DCS_MWI_TYPE_FAX               = 0x01;
 const PDU_DCS_MWI_TYPE_EMAIL             = 0x02;
 const PDU_DCS_MWI_TYPE_OTHER             = 0x03;
 

--- a/dom/system/gonk/ril_worker.js
+++ b/dom/system/gonk/ril_worker.js
@@ -5125,99 +5125,99 @@ let GsmPDUHelper = {
    *        message object for output.
    *
    * @see 3GPP TS 23.040 9.2.3.10, 3GPP TS 23.038 4.
    */
   readDataCodingScheme: function readDataCodingScheme(msg) {
     let dcs = this.readHexOctet();
     if (DEBUG) debug("PDU: read dcs: " + dcs);
 
-    // Level 2 of message waiting indication
-    this.readMessageWaitingFromDCS(msg, dcs);
-
+    // No message class by default.
+    let messageClass = PDU_DCS_MSG_CLASS_UNKNOWN;
     // 7 bit is the default fallback encoding.
     let encoding = PDU_DCS_MSG_CODING_7BITS_ALPHABET;
-    switch (dcs & 0xC0) {
-      case 0x0:
-        // bits 7..4 = 00xx
+    switch (dcs & PDU_DCS_CODING_GROUP_BITS) {
+      case 0x40: // bits 7..4 = 01xx
+      case 0x50:
+      case 0x60:
+      case 0x70:
+        // Bit 5..0 are coded exactly the same as Group 00xx
+      case 0x00: // bits 7..4 = 00xx
+      case 0x10:
+      case 0x20:
+      case 0x30:
+        if (dcs & 0x10) {
+          messageClass = dcs & PDU_DCS_MSG_CLASS_BITS;
+        }
         switch (dcs & 0x0C) {
           case 0x4:
             encoding = PDU_DCS_MSG_CODING_8BITS_ALPHABET;
             break;
           case 0x8:
             encoding = PDU_DCS_MSG_CODING_16BITS_ALPHABET;
             break;
         }
         break;
-      case 0xC0:
-        // bits 7..4 = 11xx
-        switch (dcs & 0x30) {
-          case 0x20:
-            encoding = PDU_DCS_MSG_CODING_16BITS_ALPHABET;
+
+      case 0xE0: // bits 7..4 = 1110
+        encoding = PDU_DCS_MSG_CODING_16BITS_ALPHABET;
+        // Bit 3..0 are coded exactly the same as Message Waiting Indication
+        // Group 1101.
+      case 0xC0: // bits 7..4 = 1100
+      case 0xD0: // bits 7..4 = 1101
+        // Indiciates voicemail indicator set or clear
+        let active = (dcs & PDU_DCS_MWI_ACTIVE_BITS) == PDU_DCS_MWI_ACTIVE_VALUE;
+
+        // If TP-UDH is present, these values will be overwritten
+        switch (dcs & PDU_DCS_MWI_TYPE_BITS) {
+          case PDU_DCS_MWI_TYPE_VOICEMAIL:
+            let mwi = msg.mwi;
+            if (!mwi) {
+              mwi = msg.mwi = {};
+            }
+
+            mwi.active = active;
+            mwi.discard = (dcs & PDU_DCS_CODING_GROUP_BITS) == 0xC0;
+            mwi.msgCount = active ? GECKO_VOICEMAIL_MESSAGE_COUNT_UNKNOWN : 0;
+
+            if (DEBUG) {
+              debug("MWI in DCS received for voicemail: " + JSON.stringify(mwi));
+            }
             break;
-          case 0x30:
-            if (dcs & 0x04) {
-              encoding = PDU_DCS_MSG_CODING_8BITS_ALPHABET;
-            }
+          case PDU_DCS_MWI_TYPE_FAX:
+            if (DEBUG) debug("MWI in DCS received for fax");
+            break;
+          case PDU_DCS_MWI_TYPE_EMAIL:
+            if (DEBUG) debug("MWI in DCS received for email");
+            break;
+          default:
+            if (DEBUG) debug("MWI in DCS received for \"other\"");
             break;
         }
         break;
+
+      case 0xF0: // bits 7..4 = 1111
+        if (dcs & 0x04) {
+          encoding = PDU_DCS_MSG_CODING_8BITS_ALPHABET;
+        }
+        messageClass = dcs & PDU_DCS_MSG_CLASS_BITS;
+        break;
+
       default:
         // Falling back to default encoding.
         break;
     }
 
     msg.dcs = dcs;
     msg.encoding = encoding;
+    msg.messageClass = messageClass;
 
     if (DEBUG) debug("PDU: message encoding is " + encoding + " bit.");
   },
 
-  readMessageWaitingFromDCS: function readMessageWaitingFromDCS(msg, dcs) {
-    // 0xC0 == 7 bit, don't store
-    // 0xD0 == 7 bit, store
-    // 0xE0 == UCS-2, store
-    let codingGroup = dcs & PDU_DCS_CODING_GROUP_BITS;
-
-    if (codingGroup == PDU_DCS_CODING_GROUP_7BITS_DISCARD ||
-        codingGroup == PDU_DCS_CODING_GROUP_7BITS_STORE ||
-        codingGroup == PDU_DCS_CODING_GROUP_16BITS_STORE) {
-
-      // Indiciates voicemail indicator set or clear
-      let active = (dcs & PDU_DCS_MWI_ACTIVE_BITS) == PDU_DCS_MWI_ACTIVE_VALUE;
-
-      // If TP-UDH is present, these values will be overwritten
-      switch (dcs & PDU_DCS_MWI_TYPE_BITS) {
-        case PDU_DCS_MWI_TYPE_VOICEMAIL:
-          let mwi = msg.mwi;
-          if (!mwi) {
-            mwi = msg.mwi = {};
-          }
-
-          mwi.active = active;
-          mwi.discard = codingGroup == PDU_DCS_CODING_GROUP_7BITS_DISCARD;
-          mwi.msgCount = active ? GECKO_VOICEMAIL_MESSAGE_COUNT_UNKNOWN : 0;
-
-          if (DEBUG) {
-            debug("MWI in DCS received for voicemail: " + JSON.stringify(mwi));
-          }
-          break;
-        case PDU_DCS_MWI_TYPE_FAX:
-          if (DEBUG) debug("MWI in DCS received for fax");
-          break;
-        case PDU_DCS_MWI_TYPE_EMAIL:
-          if (DEBUG) debug("MWI in DCS received for email");
-          break;
-        default:
-          if (DEBUG) debug("MWI in DCS received for \"other\"");
-          break;
-      }
-    }
-  },
-
   /**
    * Read GSM TP-Service-Centre-Time-Stamp(TP-SCTS).
    *
    * @see 3GPP TS 23.040 9.2.3.11
    */
   readTimestamp: function readTimestamp() {
     let year   = this.readSwappedNibbleBcdNum(1) + PDU_TIMESTAMP_YEAR_OFFSET;
     let month  = this.readSwappedNibbleBcdNum(1) - 1;