diff --git a/src/com/android/messaging/datamodel/DataModelImpl.java b/src/com/android/messaging/datamodel/DataModelImpl.java
index 106bfba..5d2217d 100644
--- a/src/com/android/messaging/datamodel/DataModelImpl.java
+++ b/src/com/android/messaging/datamodel/DataModelImpl.java
@@ -66,11 +66,11 @@
     private final DatabaseHelper mDatabaseHelper;
     private final SyncManager mSyncManager;
 
-    // Cached ConnectivityUtil instance for Pre-L_MR1
-    private static ConnectivityUtil sConnectivityUtilInstanceCachePreLMR1 = null;
-    // Cached ConnectivityUtil subId->instance for L_MR1 and beyond
+    // Cached ConnectivityUtil instance for Pre-N.
+    private static ConnectivityUtil sConnectivityUtilInstanceCachePreN = null;
+    // Cached ConnectivityUtil subId->instance for N and beyond
     private static final ConcurrentHashMap<Integer, ConnectivityUtil>
-            sConnectivityUtilInstanceCacheLMR1 = new ConcurrentHashMap<>();
+            sConnectivityUtilInstanceCacheN = new ConcurrentHashMap<>();
 
     public DataModelImpl(final Context context) {
         super();
@@ -79,10 +79,10 @@
         mDataModelWorker = new BackgroundWorker();
         mDatabaseHelper = DatabaseHelper.getInstance(context);
         mSyncManager = new SyncManager();
-        if (OsUtil.isAtLeastL_MR1()) {
-            createConnectivityUtilForLMR1();
+        if (OsUtil.isAtLeastN()) {
+            createConnectivityUtilForEachActiveSubscription();
         } else {
-            sConnectivityUtilInstanceCachePreLMR1 = new ConnectivityUtil(context);
+            sConnectivityUtilInstanceCachePreN = new ConnectivityUtil(context);
         }
     }
 
@@ -236,13 +236,15 @@
                             // gracefully
                             MmsConfig.loadAsync();
                             ParticipantRefresh.refreshSelfParticipants();
-                            createConnectivityUtilForLMR1();
+                            if (OsUtil.isAtLeastN()) {
+                                createConnectivityUtilForEachActiveSubscription();
+                            }
                         }
                     });
         }
     }
 
-    private void createConnectivityUtilForLMR1() {
+    private void createConnectivityUtilForEachActiveSubscription() {
         PhoneUtils.forEachActiveSubscription(new PhoneUtils.SubscriptionRunnable() {
             @Override
             public void runForSubscription(int subId) {
@@ -250,20 +252,17 @@
                 if (subId <= ParticipantData.DEFAULT_SELF_SUB_ID) {
                     subId = PhoneUtils.getDefault().getDefaultSmsSubscriptionId();
                 }
-
-                if (!sConnectivityUtilInstanceCacheLMR1.containsKey(subId)) {
-                    sConnectivityUtilInstanceCacheLMR1.put(
-                            subId, new ConnectivityUtil(mContext, subId));
-                }
+                sConnectivityUtilInstanceCacheN.computeIfAbsent(
+                        subId, key -> new ConnectivityUtil(mContext, key));
             }
         });
     }
 
     public static ConnectivityUtil getConnectivityUtil(final int subId) {
-        if (OsUtil.isAtLeastL_MR1()) {
-            return sConnectivityUtilInstanceCacheLMR1.get(subId);
+        if (OsUtil.isAtLeastN()) {
+            return sConnectivityUtilInstanceCacheN.get(subId);
         } else {
-            return sConnectivityUtilInstanceCachePreLMR1;
+            return sConnectivityUtilInstanceCachePreN;
         }
     }
 }
diff --git a/src/com/android/messaging/util/ConnectivityUtil.java b/src/com/android/messaging/util/ConnectivityUtil.java
index 0229607..a7467e4 100644
--- a/src/com/android/messaging/util/ConnectivityUtil.java
+++ b/src/com/android/messaging/util/ConnectivityUtil.java
@@ -23,6 +23,16 @@
 
 import com.android.messaging.datamodel.data.ParticipantData;
 
+/**
+ * ConnectivityUtil listens to the network service state changes.
+ *
+ * On N and beyond, This class instance can be created via ConnectivityUtil(context, subId), use
+ * ConnectivityUtil(context) for others.
+ *
+ * Note that TelephonyManager has createForSubscriptionId() for a specific subId from N but listen()
+ * does not use the subId on the manager, and uses the default subId on PhoneStateListener. From O,
+ * the manager uses its' own subId in listen().
+ */
 public class ConnectivityUtil {
     // Assume not connected until informed differently
     private volatile int mCurrentServiceState = ServiceState.STATE_POWER_OFF;
@@ -40,6 +50,7 @@
     }
 
     public ConnectivityUtil(final Context context, final int subId) {
+        Assert.isTrue(OsUtil.isAtLeastN());
         mTelephonyManager =
                 ((TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE))
                         .createForSubscriptionId(subId);