diff --git a/b2g/chrome/content/settings.js b/b2g/chrome/content/settings.js
index 7400a67873c8..8459611668d6 100644
--- a/b2g/chrome/content/settings.js
+++ b/b2g/chrome/content/settings.js
@@ -157,6 +157,16 @@ SettingsListener.observe('language.current', 'en-US', function(value) {
     function(value) {
       Services.prefs.setCharPref('wap.UAProf.tagname', value);
   });
+
+  // DSDS default service IDs
+  ['mms', 'sms', 'telephony', 'voicemail'].forEach(function(key) {
+    SettingsListener.observe('ril.' + key + '.defaultServiceId', 0,
+                             function(value) {
+      if (value != null) {
+        Services.prefs.setIntPref('dom.' + key + '.defaultServiceId', value);
+      }
+    });
+  });
 })();
 
 //=================== DeviceInfo ====================
diff --git a/dom/mobilemessage/src/android/MmsService.cpp b/dom/mobilemessage/src/android/MmsService.cpp
index fba2a2e358de..06df6effb37a 100644
--- a/dom/mobilemessage/src/android/MmsService.cpp
+++ b/dom/mobilemessage/src/android/MmsService.cpp
@@ -14,6 +14,13 @@ namespace mobilemessage {
 
 NS_IMPL_ISUPPORTS1(MmsService, nsIMmsService)
 
+NS_IMETHODIMP
+MmsService::GetMmsDefaultServiceId(uint32_t* aServiceId)
+{
+  NS_NOTYETIMPLEMENTED("Implement me!");
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
 NS_IMETHODIMP
 MmsService::Send(const JS::Value& aParameters,
                  nsIMobileMessageCallback *aRequest)
diff --git a/dom/mobilemessage/src/android/SmsService.cpp b/dom/mobilemessage/src/android/SmsService.cpp
index 1da4b0a7ead8..f3a455fb6bc9 100644
--- a/dom/mobilemessage/src/android/SmsService.cpp
+++ b/dom/mobilemessage/src/android/SmsService.cpp
@@ -15,6 +15,14 @@ namespace mobilemessage {
 
 NS_IMPL_ISUPPORTS1(SmsService, nsISmsService)
 
+NS_IMETHODIMP
+SmsService::GetSmsDefaultServiceId(uint32_t* aServiceId)
+{
+  // Android has no official DSDS support.
+  *aServiceId = 0;
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 SmsService::HasSupport(bool* aHasSupport)
 {
diff --git a/dom/mobilemessage/src/fallback/MmsService.cpp b/dom/mobilemessage/src/fallback/MmsService.cpp
index f49151aa04b1..11d5bcebed4b 100644
--- a/dom/mobilemessage/src/fallback/MmsService.cpp
+++ b/dom/mobilemessage/src/fallback/MmsService.cpp
@@ -13,6 +13,13 @@ namespace mobilemessage {
 
 NS_IMPL_ISUPPORTS1(MmsService, nsIMmsService)
 
+NS_IMETHODIMP
+MmsService::GetMmsDefaultServiceId(uint32_t* aServiceId)
+{
+  NS_NOTYETIMPLEMENTED("Implement me!");
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
 NS_IMETHODIMP
 MmsService::Send(const JS::Value& aParameters,
                  nsIMobileMessageCallback *aRequest)
diff --git a/dom/mobilemessage/src/fallback/SmsService.cpp b/dom/mobilemessage/src/fallback/SmsService.cpp
index a04a46765491..b4595a5e800a 100644
--- a/dom/mobilemessage/src/fallback/SmsService.cpp
+++ b/dom/mobilemessage/src/fallback/SmsService.cpp
@@ -14,6 +14,13 @@ namespace mobilemessage {
 
 NS_IMPL_ISUPPORTS1(SmsService, nsISmsService)
 
+NS_IMETHODIMP
+SmsService::GetSmsDefaultServiceId(uint32_t* aServiceId)
+{
+  NS_ERROR("We should not be here!");
+  return NS_ERROR_FAILURE;
+}
+
 NS_IMETHODIMP
 SmsService::HasSupport(bool* aHasSupport)
 {
diff --git a/dom/mobilemessage/src/gonk/MmsService.js b/dom/mobilemessage/src/gonk/MmsService.js
index 7e2610c3d309..c619043e97e3 100644
--- a/dom/mobilemessage/src/gonk/MmsService.js
+++ b/dom/mobilemessage/src/gonk/MmsService.js
@@ -108,6 +108,9 @@ const PREF_RETRIEVAL_RETRY_INTERVALS = (function () {
   return intervals;
 })();
 
+const kPrefRilNumRadioInterfaces = "ril.numRadioInterfaces";
+const kPrefDefaultServiceId = "dom.mms.defaultServiceId";
+
 XPCOMUtils.defineLazyServiceGetter(this, "gpps",
                                    "@mozilla.org/network/protocol-proxy-service;1",
                                    "nsIProtocolProxyService");
@@ -1189,6 +1192,17 @@ AcknowledgeTransaction.prototype = {
   }
 };
 
+function getDefaultServiceId() {
+  let id = Services.prefs.getIntPref(kPrefDefaultServiceId);
+  let numRil = Services.prefs.getIntPref(kPrefRilNumRadioInterfaces);
+
+  if (id >= numRil || id < 0) {
+    id = 0;
+  }
+
+  return id;
+}
+
 /**
  * MmsService
  */
@@ -1199,13 +1213,17 @@ function MmsService() {
     debug("Running protocol version: " + macro + "." + minor);
   }
 
+  Services.prefs.addObserver(kPrefDefaultServiceId, this, false);
+  this.mmsDefaultServiceId = getDefaultServiceId();
+
   // TODO: bug 810084 - support application identifier
 }
 MmsService.prototype = {
 
   classID:   RIL_MMSSERVICE_CID,
   QueryInterface: XPCOMUtils.generateQI([Ci.nsIMmsService,
-                                         Ci.nsIWapPushApplication]),
+                                         Ci.nsIWapPushApplication,
+                                         Ci.nsIObserver]),
   /*
    * Whether or not should we enable X-Mms-Report-Allowed in M-NotifyResp.ind
    * and M-Acknowledge.ind PDU.
@@ -1801,6 +1819,8 @@ MmsService.prototype = {
 
   // nsIMmsService
 
+  mmsDefaultServiceId: 0,
+
   send: function send(aParams, aRequest) {
     if (DEBUG) debug("send: aParams: " + JSON.stringify(aParams));
 
@@ -2111,6 +2131,18 @@ MmsService.prototype = {
         break;
     }
   },
+
+  // nsIObserver
+
+  observe: function observe(aSubject, aTopic, aData) {
+    switch (aTopic) {
+      case NS_PREFBRANCH_PREFCHANGE_TOPIC_ID:
+        if (aData === kPrefDefaultServiceId) {
+          this.mmsDefaultServiceId = getDefaultServiceId();
+        }
+        break;
+    }
+  }
 };
 
 this.NSGetFactory = XPCOMUtils.generateNSGetFactory([MmsService]);
diff --git a/dom/mobilemessage/src/gonk/SmsService.cpp b/dom/mobilemessage/src/gonk/SmsService.cpp
index a61382356883..4b25015f60f1 100644
--- a/dom/mobilemessage/src/gonk/SmsService.cpp
+++ b/dom/mobilemessage/src/gonk/SmsService.cpp
@@ -7,13 +7,40 @@
 #include "SmsService.h"
 #include "jsapi.h"
 #include "SmsSegmentInfo.h"
+#include "mozilla/Preferences.h"
 #include "nsServiceManagerUtils.h"
 
+namespace {
+
+const char* kPrefRilNumRadioInterfaces = "ril.numRadioInterfaces";
+#define kPrefDefaultServiceId "dom.sms.defaultServiceId"
+const char* kObservedPrefs[] = {
+  kPrefDefaultServiceId,
+  nullptr
+};
+
+uint32_t
+getDefaultServiceId()
+{
+  int32_t id = mozilla::Preferences::GetInt(kPrefDefaultServiceId, 0);
+  int32_t numRil = mozilla::Preferences::GetInt(kPrefRilNumRadioInterfaces, 1);
+
+  if (id >= numRil || id < 0) {
+    id = 0;
+  }
+
+  return id;
+}
+
+} // Anonymous namespace
+
 namespace mozilla {
 namespace dom {
 namespace mobilemessage {
 
-NS_IMPL_ISUPPORTS1(SmsService, nsISmsService)
+NS_IMPL_ISUPPORTS2(SmsService,
+                   nsISmsService,
+                   nsIObserver)
 
 SmsService::SmsService()
 {
@@ -22,6 +49,42 @@ SmsService::SmsService()
     ril->GetRadioInterface(0, getter_AddRefs(mRadioInterface));
   }
   NS_WARN_IF_FALSE(mRadioInterface, "This shouldn't fail!");
+
+  // Initialize observer.
+  Preferences::AddStrongObservers(this, kObservedPrefs);
+  mDefaultServiceId = getDefaultServiceId();
+}
+
+/*
+ * Implementation of nsIObserver.
+ */
+
+NS_IMETHODIMP
+SmsService::Observe(nsISupports* aSubject,
+                    const char* aTopic,
+                    const PRUnichar* aData)
+{
+  if (!strcmp(aTopic, NS_PREFBRANCH_PREFCHANGE_TOPIC_ID)) {
+    nsDependentString data(aData);
+    if (data.EqualsLiteral(kPrefDefaultServiceId)) {
+      mDefaultServiceId = getDefaultServiceId();
+    }
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(false, "SmsService got unexpected topic!");
+  return NS_ERROR_UNEXPECTED;
+}
+
+/*
+ * Implementation of nsISmsService.
+ */
+
+NS_IMETHODIMP
+SmsService::GetSmsDefaultServiceId(uint32_t* aServiceId)
+{
+  *aServiceId = mDefaultServiceId;
+  return NS_OK;
 }
 
 NS_IMETHODIMP
diff --git a/dom/mobilemessage/src/gonk/SmsService.h b/dom/mobilemessage/src/gonk/SmsService.h
index a75512dbb863..8b3620be7070 100644
--- a/dom/mobilemessage/src/gonk/SmsService.h
+++ b/dom/mobilemessage/src/gonk/SmsService.h
@@ -7,6 +7,7 @@
 
 #include "nsISmsService.h"
 #include "nsCOMPtr.h"
+#include "nsIObserver.h"
 #include "nsIRadioInterfaceLayer.h"
 #include "nsTArray.h"
 #include "nsString.h"
@@ -17,16 +18,20 @@ namespace dom {
 namespace mobilemessage {
 
 class SmsService MOZ_FINAL : public nsISmsService
+                           , public nsIObserver
 {
 public:
   NS_DECL_ISUPPORTS
   NS_DECL_NSISMSSERVICE
+  NS_DECL_NSIOBSERVER
+
   SmsService();
 
 protected:
   // TODO: Bug 854326 - B2G Multi-SIM: support multiple SIM cards for SMS/MMS
   nsCOMPtr<nsIRadioInterface> mRadioInterface;
   nsTArray<nsString> mSilentNumbers;
+  uint32_t mDefaultServiceId;
 };
 
 } // namespace mobilemessage
diff --git a/dom/mobilemessage/src/ipc/SmsIPCService.cpp b/dom/mobilemessage/src/ipc/SmsIPCService.cpp
index 876bb2a2f4fc..9180dccc1d5f 100644
--- a/dom/mobilemessage/src/ipc/SmsIPCService.cpp
+++ b/dom/mobilemessage/src/ipc/SmsIPCService.cpp
@@ -17,12 +17,23 @@
 #include "mozilla/dom/MobileMessageManagerBinding.h"
 #include "mozilla/dom/MozMmsMessageBinding.h"
 #include "mozilla/dom/BindingUtils.h"
+#include "mozilla/Preferences.h"
+#include "nsString.h"
 
 using namespace mozilla::dom;
 using namespace mozilla::dom::mobilemessage;
 
 namespace {
 
+const char* kPrefRilNumRadioInterfaces = "ril.numRadioInterfaces";
+#define kPrefMmsDefaultServiceId "dom.mms.defaultServiceId"
+#define kPrefSmsDefaultServiceId "dom.sms.defaultServiceId"
+const char* kObservedPrefs[] = {
+  kPrefMmsDefaultServiceId,
+  kPrefSmsDefaultServiceId,
+  nullptr
+};
+
 // TODO: Bug 767082 - WebSMS: sSmsChild leaks at shutdown
 PSmsChild* gSmsChild;
 
@@ -74,16 +85,69 @@ SendCursorRequest(const IPCMobileMessageCursor& aRequest,
   actor.forget(aResult);
   return NS_OK;
 }
+
+uint32_t
+getDefaultServiceId(const char* aPrefKey)
+{
+  int32_t id = mozilla::Preferences::GetInt(aPrefKey, 0);
+  int32_t numRil = mozilla::Preferences::GetInt(kPrefRilNumRadioInterfaces, 1);
+
+  if (id >= numRil || id < 0) {
+    id = 0;
+  }
+
+  return id;
+}
+
 } // anonymous namespace
 
-NS_IMPL_ISUPPORTS3(SmsIPCService,
+NS_IMPL_ISUPPORTS4(SmsIPCService,
                    nsISmsService,
                    nsIMmsService,
-                   nsIMobileMessageDatabaseService)
+                   nsIMobileMessageDatabaseService,
+                   nsIObserver)
+
+SmsIPCService::SmsIPCService()
+{
+  Preferences::AddStrongObservers(this, kObservedPrefs);
+  mMmsDefaultServiceId = getDefaultServiceId(kPrefMmsDefaultServiceId);
+  mSmsDefaultServiceId = getDefaultServiceId(kPrefSmsDefaultServiceId);
+}
+
+/*
+ * Implementation of nsIObserver.
+ */
+
+NS_IMETHODIMP
+SmsIPCService::Observe(nsISupports* aSubject,
+                       const char* aTopic,
+                       const PRUnichar* aData)
+{
+  if (!strcmp(aTopic, NS_PREFBRANCH_PREFCHANGE_TOPIC_ID)) {
+    nsDependentString data(aData);
+    if (data.EqualsLiteral(kPrefMmsDefaultServiceId)) {
+      mMmsDefaultServiceId = getDefaultServiceId(kPrefMmsDefaultServiceId);
+    } else if (data.EqualsLiteral(kPrefSmsDefaultServiceId)) {
+      mSmsDefaultServiceId = getDefaultServiceId(kPrefSmsDefaultServiceId);
+    }
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(false, "SmsIPCService got unexpected topic!");
+  return NS_ERROR_UNEXPECTED;
+}
 
 /*
  * Implementation of nsISmsService.
  */
+
+NS_IMETHODIMP
+SmsIPCService::GetSmsDefaultServiceId(uint32_t* aServiceId)
+{
+  *aServiceId = mSmsDefaultServiceId;
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 SmsIPCService::HasSupport(bool* aHasSupport)
 {
@@ -236,6 +300,17 @@ GetSendMmsMessageRequestFromParams(const JS::Value& aParam,
   return true;
 }
 
+/*
+ * Implementation of nsIMmsService.
+ */
+
+NS_IMETHODIMP
+SmsIPCService::GetMmsDefaultServiceId(uint32_t* aServiceId)
+{
+  *aServiceId = mMmsDefaultServiceId;
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 SmsIPCService::Send(const JS::Value& aParameters,
                     nsIMobileMessageCallback *aRequest)
diff --git a/dom/mobilemessage/src/ipc/SmsIPCService.h b/dom/mobilemessage/src/ipc/SmsIPCService.h
index 98b9a7737efd..8fbc12c7660e 100644
--- a/dom/mobilemessage/src/ipc/SmsIPCService.h
+++ b/dom/mobilemessage/src/ipc/SmsIPCService.h
@@ -9,6 +9,7 @@
 #include "nsISmsService.h"
 #include "nsIMmsService.h"
 #include "nsIMobileMessageDatabaseService.h"
+#include "nsIObserver.h"
 #include "mozilla/Attributes.h"
 
 namespace mozilla {
@@ -20,12 +21,20 @@ class PSmsChild;
 class SmsIPCService MOZ_FINAL : public nsISmsService
                               , public nsIMmsService
                               , public nsIMobileMessageDatabaseService
+                              , public nsIObserver
 {
 public:
   NS_DECL_ISUPPORTS
   NS_DECL_NSISMSSERVICE
   NS_DECL_NSIMMSSERVICE
   NS_DECL_NSIMOBILEMESSAGEDATABASESERVICE
+  NS_DECL_NSIOBSERVER
+
+  SmsIPCService();
+
+private:
+  uint32_t mMmsDefaultServiceId;
+  uint32_t mSmsDefaultServiceId;
 };
 
 } // namespace mobilemessage
diff --git a/dom/system/gonk/RILContentHelper.js b/dom/system/gonk/RILContentHelper.js
index 3feb403f1671..fd60d57a95e0 100644
--- a/dom/system/gonk/RILContentHelper.js
+++ b/dom/system/gonk/RILContentHelper.js
@@ -29,7 +29,9 @@ const NS_XPCOM_SHUTDOWN_OBSERVER_ID = "xpcom-shutdown";
 
 const NS_PREFBRANCH_PREFCHANGE_TOPIC_ID = "nsPref:changed";
 
+const kPrefRilNumRadioInterfaces = "ril.numRadioInterfaces";
 const kPrefRilDebuggingEnabled = "ril.debugging.enabled";
+const kPrefVoicemailDefaultServiceId = "dom.voicemail.defaultServiceId";
 
 let DEBUG;
 function debug(s) {
@@ -119,8 +121,7 @@ XPCOMUtils.defineLazyGetter(this, "gNumRadioInterfaces", function () {
     return ril.numRadioInterfaces;
   }
 
-  let num = cpmm.sendSyncMessage("RIL:GetNumRadioInterfaces")[0];
-  return num;
+  return Services.prefs.getIntPref(kPrefRilNumRadioInterfaces);
 });
 
 function MobileIccCardLockResult(options) {
@@ -452,6 +453,7 @@ function RILContentHelper() {
     dataConnectionInfo:   new MobileConnectionInfo()
   };
   this.voicemailInfo = new VoicemailInfo();
+  this.voicemailDefaultServiceId = this.getVoicemailDefaultServiceId();
 
   this.initDOMRequestHelper(/* aWindow */ null, RIL_IPC_MSG_NAMES);
   this._windowsMap = [];
@@ -459,6 +461,7 @@ function RILContentHelper() {
   Services.obs.addObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID, false);
 
   Services.prefs.addObserver(kPrefRilDebuggingEnabled, this, false);
+  Services.prefs.addObserver(kPrefVoicemailDefaultServiceId, this, false);
 }
 
 RILContentHelper.prototype = {
@@ -1318,6 +1321,17 @@ RILContentHelper.prototype = {
 
   voicemailStatus: null,
 
+  voicemailDefaultServiceId: 0,
+  getVoicemailDefaultServiceId: function getVoicemailDefaultServiceId() {
+    let id = Services.prefs.getIntPref(kPrefVoicemailDefaultServiceId);
+
+    if (id >= gNumRadioInterfaces || id < 0) {
+      id = 0;
+    }
+
+    return id;
+  },
+
   getVoicemailInfo: function getVoicemailInfo() {
     // Get voicemail infomation by IPC only on first time.
     this.getVoicemailInfo = function getVoicemailInfo() {
@@ -1332,9 +1346,11 @@ RILContentHelper.prototype = {
 
     return this.voicemailInfo;
   },
+
   get voicemailNumber() {
     return this.getVoicemailInfo().number;
   },
+
   get voicemailDisplayName() {
     return this.getVoicemailInfo().displayName;
   },
@@ -1413,6 +1429,8 @@ RILContentHelper.prototype = {
       case NS_PREFBRANCH_PREFCHANGE_TOPIC_ID:
         if (data == kPrefRilDebuggingEnabled) {
           this.updateDebugFlag();
+        } else if (data == kPrefVoicemailDefaultServiceId) {
+          this.voicemailDefaultServiceId = this.getVoicemailDefaultServiceId();
         }
         break;
 
diff --git a/dom/system/gonk/RadioInterfaceLayer.js b/dom/system/gonk/RadioInterfaceLayer.js
index 6eb28463b2f2..ead6f59abe58 100644
--- a/dom/system/gonk/RadioInterfaceLayer.js
+++ b/dom/system/gonk/RadioInterfaceLayer.js
@@ -76,6 +76,7 @@ const NS_PREFBRANCH_PREFCHANGE_TOPIC_ID = "nsPref:changed";
 
 const kPrefCellBroadcastDisabled = "ril.cellbroadcast.disabled";
 const kPrefClirModePreference = "ril.clirMode";
+const kPrefRilNumRadioInterfaces = "ril.numRadioInterfaces";
 
 const DOM_MOBILE_MESSAGE_DELIVERY_RECEIVED = "received";
 const DOM_MOBILE_MESSAGE_DELIVERY_SENDING  = "sending";
@@ -86,7 +87,6 @@ const RADIO_POWER_OFF_TIMEOUT = 30000;
 const SMS_HANDLED_WAKELOCK_TIMEOUT = 5000;
 
 const RIL_IPC_MOBILECONNECTION_MSG_NAMES = [
-  "RIL:GetNumRadioInterfaces",
   "RIL:GetRilContext",
   "RIL:GetAvailableNetworks",
   "RIL:SelectNetwork",
@@ -111,7 +111,6 @@ const RIL_IPC_MOBILECONNECTION_MSG_NAMES = [
 ];
 
 const RIL_IPC_ICCMANAGER_MSG_NAMES = [
-  "RIL:GetNumRadioInterfaces",
   "RIL:SendStkResponse",
   "RIL:SendStkMenuSelection",
   "RIL:SendStkTimerExpiration",
@@ -129,13 +128,11 @@ const RIL_IPC_ICCMANAGER_MSG_NAMES = [
 ];
 
 const RIL_IPC_VOICEMAIL_MSG_NAMES = [
-  "RIL:GetNumRadioInterfaces",
   "RIL:RegisterVoicemailMsg",
   "RIL:GetVoicemailInfo"
 ];
 
 const RIL_IPC_CELLBROADCAST_MSG_NAMES = [
-  "RIL:GetNumRadioInterfaces",
   "RIL:RegisterCellBroadcastMsg"
 ];
 
@@ -399,8 +396,6 @@ XPCOMUtils.defineLazyGetter(this, "gMessageManager", function () {
       }
 
       switch (msg.name) {
-        case "RIL:GetNumRadioInterfaces":
-          return this.ril.numRadioInterfaces;
         case "RIL:RegisterMobileConnectionMsg":
           this._registerMessageTarget("mobileconnection", msg.target);
           return null;
@@ -471,6 +466,25 @@ XPCOMUtils.defineLazyGetter(this, "gMessageManager", function () {
   };
 });
 
+// Initialize shared preference 'ril.numRadioInterfaces' according to system
+// property.
+try {
+  Services.prefs.setIntPref(kPrefRilNumRadioInterfaces, (function () {
+    // When Gonk property "ro.moz.ril.numclients" is not set, return 1; if
+    // explicitly set to any number larger-equal than 0, return num; else, return
+    // 1 for compatibility.
+    try {
+      let numString = libcutils.property_get("ro.moz.ril.numclients", "1");
+      let num = parseInt(numString, 10);
+      if (num >= 0) {
+        return num;
+      }
+    } catch (e) {}
+
+    return 1;
+  })());
+} catch (e) {}
+
 function IccInfo() {}
 IccInfo.prototype = {
   iccType: null,
@@ -572,16 +586,9 @@ RadioInterfaceLayer.prototype = {
 
 XPCOMUtils.defineLazyGetter(RadioInterfaceLayer.prototype,
                             "numRadioInterfaces", function () {
-  // When Gonk property "ro.moz.ril.numclients" is not set, return 1; if
-  // explicitly set to any number larger-equal than 0, return num; else, return
-  // 1 for compatibility.
   try {
-    let numString = libcutils.property_get("ro.moz.ril.numclients", "1");
-    let num = parseInt(numString, 10);
-    if (num >= 0) {
-      return num;
-    }
-  } catch (e) {}
+    return Services.prefs.getIntPref(kPrefRilNumRadioInterfaces);
+  } catch(e) {}
 
   return 1;
 });
diff --git a/dom/telephony/gonk/TelephonyProvider.js b/dom/telephony/gonk/TelephonyProvider.js
index 25488cffa14e..123011220c17 100644
--- a/dom/telephony/gonk/TelephonyProvider.js
+++ b/dom/telephony/gonk/TelephonyProvider.js
@@ -22,7 +22,9 @@ const NS_XPCOM_SHUTDOWN_OBSERVER_ID   = "xpcom-shutdown";
 
 const NS_PREFBRANCH_PREFCHANGE_TOPIC_ID = "nsPref:changed";
 
+const kPrefRilNumRadioInterfaces = "ril.numRadioInterfaces";
 const kPrefRilDebuggingEnabled = "ril.debugging.enabled";
+const kPrefDefaultServiceId = "dom.telephony.defaultServiceId";
 
 const nsIAudioManager = Ci.nsIAudioManager;
 const nsITelephonyProvider = Ci.nsITelephonyProvider;
@@ -86,8 +88,10 @@ function TelephonyProvider() {
   this._listeners = [];
 
   this._updateDebugFlag();
+  this.defaultServiceId = this._getDefaultServiceId();
 
   Services.prefs.addObserver(kPrefRilDebuggingEnabled, this, false);
+  Services.prefs.addObserver(kPrefDefaultServiceId, this, false);
 
   Services.obs.addObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID, false);
 }
@@ -273,10 +277,23 @@ TelephonyProvider.prototype = {
     } catch (e) {}
   },
 
+  _getDefaultServiceId: function _getDefaultServiceId() {
+    let id = Services.prefs.getIntPref(kPrefDefaultServiceId);
+    let numRil = Services.prefs.getIntPref(kPrefRilNumRadioInterfaces);
+
+    if (id >= numRil || id < 0) {
+      id = 0;
+    }
+
+    return id;
+  },
+
   /**
    * nsITelephonyProvider interface.
    */
 
+  defaultServiceId: 0,
+
   registerListener: function(aListener) {
     if (this._listeners.indexOf(aListener) >= 0) {
       throw Cr.NS_ERROR_UNEXPECTED;
@@ -513,6 +530,8 @@ TelephonyProvider.prototype = {
       case NS_PREFBRANCH_PREFCHANGE_TOPIC_ID:
         if (aData === kPrefRilDebuggingEnabled) {
           this._updateDebugFlag();
+	} else if (aData === kPrefDefaultServiceId) {
+          this.defaultServiceId = this._getDefaultServiceId();
         }
         break;
 
diff --git a/dom/telephony/ipc/TelephonyIPCProvider.cpp b/dom/telephony/ipc/TelephonyIPCProvider.cpp
index 3b40a31271c3..6da47f8face6 100644
--- a/dom/telephony/ipc/TelephonyIPCProvider.cpp
+++ b/dom/telephony/ipc/TelephonyIPCProvider.cpp
@@ -3,22 +3,52 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#include "ipc/TelephonyIPCProvider.h"
+
 #include "mozilla/dom/ContentChild.h"
 #include "mozilla/dom/telephony/TelephonyChild.h"
-#include "ipc/TelephonyIPCProvider.h"
+#include "mozilla/Preferences.h"
 
 USING_TELEPHONY_NAMESPACE
 using namespace mozilla::dom;
 
-NS_IMPL_ISUPPORTS2(TelephonyIPCProvider,
+namespace {
+
+const char* kPrefRilNumRadioInterfaces = "ril.numRadioInterfaces";
+#define kPrefDefaultServiceId "dom.telephony.defaultServiceId"
+const char* kObservedPrefs[] = {
+  kPrefDefaultServiceId,
+  nullptr
+};
+
+uint32_t
+getDefaultServiceId()
+{
+  int32_t id = mozilla::Preferences::GetInt(kPrefDefaultServiceId, 0);
+  int32_t numRil = mozilla::Preferences::GetInt(kPrefRilNumRadioInterfaces, 1);
+
+  if (id >= numRil || id < 0) {
+    id = 0;
+  }
+
+  return id;
+}
+
+} // Anonymous namespace
+
+NS_IMPL_ISUPPORTS3(TelephonyIPCProvider,
                    nsITelephonyProvider,
-                   nsITelephonyListener)
+                   nsITelephonyListener,
+                   nsIObserver)
 
 TelephonyIPCProvider::TelephonyIPCProvider()
 {
   // Deallocated in ContentChild::DeallocPTelephonyChild().
   mPTelephonyChild = new TelephonyChild(this);
   ContentChild::GetSingleton()->SendPTelephonyConstructor(mPTelephonyChild);
+
+  Preferences::AddStrongObservers(this, kObservedPrefs);
+  mDefaultServiceId = getDefaultServiceId();
 }
 
 TelephonyIPCProvider::~TelephonyIPCProvider()
@@ -27,10 +57,38 @@ TelephonyIPCProvider::~TelephonyIPCProvider()
   mPTelephonyChild = nullptr;
 }
 
+/*
+ * Implementation of nsIObserver.
+ */
+
+NS_IMETHODIMP
+TelephonyIPCProvider::Observe(nsISupports* aSubject,
+                              const char* aTopic,
+                              const PRUnichar* aData)
+{
+  if (!strcmp(aTopic, NS_PREFBRANCH_PREFCHANGE_TOPIC_ID)) {
+    nsDependentString data(aData);
+    if (data.EqualsLiteral(kPrefDefaultServiceId)) {
+      mDefaultServiceId = getDefaultServiceId();
+    }
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(false, "TelephonyIPCProvider got unexpected topic!");
+  return NS_ERROR_UNEXPECTED;
+}
+
 /*
  * Implementation of nsITelephonyProvider.
  */
 
+NS_IMETHODIMP
+TelephonyIPCProvider::GetDefaultServiceId(uint32_t* aServiceId)
+{
+  *aServiceId = mDefaultServiceId;
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 TelephonyIPCProvider::RegisterListener(nsITelephonyListener *aListener)
 {
diff --git a/dom/telephony/ipc/TelephonyIPCProvider.h b/dom/telephony/ipc/TelephonyIPCProvider.h
index 928fd1d6567c..215bc7a9deb6 100644
--- a/dom/telephony/ipc/TelephonyIPCProvider.h
+++ b/dom/telephony/ipc/TelephonyIPCProvider.h
@@ -8,6 +8,7 @@
 
 #include "mozilla/dom/telephony/TelephonyCommon.h"
 #include "mozilla/Attributes.h"
+#include "nsIObserver.h"
 #include "nsITelephonyProvider.h"
 
 BEGIN_TELEPHONY_NAMESPACE
@@ -16,11 +17,13 @@ class PTelephonyChild;
 
 class TelephonyIPCProvider MOZ_FINAL : public nsITelephonyProvider
                                      , public nsITelephonyListener
+                                     , public nsIObserver
 {
 public:
   NS_DECL_ISUPPORTS
   NS_DECL_NSITELEPHONYPROVIDER
   NS_DECL_NSITELEPHONYLISTENER
+  NS_DECL_NSIOBSERVER
 
   TelephonyIPCProvider();
 
@@ -30,6 +33,7 @@ protected:
 private:
   nsTArray<nsCOMPtr<nsITelephonyListener> > mListeners;
   PTelephonyChild* mPTelephonyChild;
+  uint32_t mDefaultServiceId;
 };
 
 END_TELEPHONY_NAMESPACE
diff --git a/modules/libpref/src/init/all.js b/modules/libpref/src/init/all.js
index d2b84cf01cc6..eab693dcba9f 100644
--- a/modules/libpref/src/init/all.js
+++ b/modules/libpref/src/init/all.js
@@ -4300,7 +4300,9 @@ pref("dom.sms.enabled", false);
 // 7-bit default alphabet.
 pref("dom.sms.strict7BitEncoding", false);
 pref("dom.sms.requestStatusReport", true);
-pref("dom.mms.requestStatusReport", true);
+// Numeric default service id for SMS API calls with |serviceId| parameter
+// omitted.
+pref("dom.sms.defaultServiceId", 0);
 
 // WebContacts
 pref("dom.mozContacts.enabled", false);
@@ -4426,6 +4428,8 @@ pref("wap.UAProf.tagname", "x-wap-profile");
 // @see OMA-TS-MMS_ENC-V1_3-20110913-A clause 7.3.34
 pref("dom.mms.version", 19);
 
+pref("dom.mms.requestStatusReport", true);
+
 // Retrieval mode for MMS
 // manual: Manual retrieval mode.
 // automatic: Automatic retrieval mode even in roaming.
@@ -4438,10 +4442,15 @@ pref("dom.mms.sendRetryInterval", 300000);
 
 pref("dom.mms.retrievalRetryCount", 4);
 pref("dom.mms.retrievalRetryIntervals", "60000,300000,600000,1800000");
-
+// Numeric default service id for MMS API calls with |serviceId| parameter
+// omitted.
+pref("dom.mms.defaultServiceId", 0);
 // Debug enabler for MMS.
 pref("mms.debugging.enabled", false);
 
+// Number of RadioInterface instances to create.
+pref("ril.numRadioInterfaces", 0);
+
 // If the user puts a finger down on an element and we think the user
 // might be executing a pan gesture, how long do we wait before
 // tentatively deciding the gesture is actually a tap and activating
@@ -4477,6 +4486,9 @@ pref("dom.datastore.enabled", false);
 
 // Telephony API
 pref("dom.telephony.enabled", false);
+// Numeric default service id for WebTelephony API calls with |serviceId|
+// parameter omitted.
+pref("dom.telephony.defaultServiceId", 0);
 
 // Cell Broadcast API
 pref("dom.cellbroadcast.enabled", false);
@@ -4489,6 +4501,9 @@ pref("dom.mobileconnection.enabled", false);
 
 // Voice Mail API
 pref("dom.voicemail.enabled", false);
+// Numeric default service id for Voice Mail API calls with |serviceId|
+// parameter omitted.
+pref("dom.voicemail.defaultServiceId", 0);
 
 // DOM Inter-App Communication API.
 pref("dom.inter-app-communication-api.enabled", false);