diff --git a/telecomm/java/android/telecomm/Call.java b/telecomm/java/android/telecomm/Call.java
index f988ac8..7223574 100644
--- a/telecomm/java/android/telecomm/Call.java
+++ b/telecomm/java/android/telecomm/Call.java
@@ -27,6 +27,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.concurrent.CopyOnWriteArrayList;
 
 /**
  * Represents an ongoing phone call that the in-call app should present to the user.
@@ -364,7 +365,7 @@
     private final InCallAdapter mInCallAdapter;
     private final List<Call> mChildren = new ArrayList<>();
     private final List<Call> mUnmodifiableChildren = Collections.unmodifiableList(mChildren);
-    private final List<Listener> mListeners = new ArrayList<>();
+    private final List<Listener> mListeners = new CopyOnWriteArrayList<>();
     private final List<Call> mConferenceableCalls = new ArrayList<>();
     private final List<Call> mUnmodifiableConferenceableCalls =
             Collections.unmodifiableList(mConferenceableCalls);
@@ -589,7 +590,9 @@
      * @param listener A {@code Listener}.
      */
     public void removeListener(Listener listener) {
-        mListeners.remove(listener);
+        if (listener != null) {
+            mListeners.remove(listener);
+        }
     }
 
     /** {@hide} */
@@ -709,72 +712,62 @@
     }
 
     private void fireStateChanged(int newState) {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onStateChanged(this, newState);
+        for (Listener listener : mListeners) {
+            listener.onStateChanged(this, newState);
         }
     }
 
     private void fireParentChanged(Call newParent) {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onParentChanged(this, newParent);
+        for (Listener listener : mListeners) {
+            listener.onParentChanged(this, newParent);
         }
     }
 
     private void fireChildrenChanged(List<Call> children) {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onChildrenChanged(this, children);
+        for (Listener listener : mListeners) {
+            listener.onChildrenChanged(this, children);
         }
     }
 
     private void fireDetailsChanged(Details details) {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onDetailsChanged(this, details);
+        for (Listener listener : mListeners) {
+            listener.onDetailsChanged(this, details);
         }
     }
 
     private void fireCannedTextResponsesLoaded(List<String> cannedTextResponses) {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onCannedTextResponsesLoaded(this, cannedTextResponses);
+        for (Listener listener : mListeners) {
+            listener.onCannedTextResponsesLoaded(this, cannedTextResponses);
         }
     }
 
     private void fireVideoCallChanged(InCallService.VideoCall videoCall) {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onVideoCallChanged(this, videoCall);
+        for (Listener listener : mListeners) {
+            listener.onVideoCallChanged(this, videoCall);
         }
     }
 
     private void firePostDialWait(String remainingPostDialSequence) {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onPostDialWait(this, remainingPostDialSequence);
+        for (Listener listener : mListeners) {
+            listener.onPostDialWait(this, remainingPostDialSequence);
         }
     }
 
     private void fireStartActivity(PendingIntent intent) {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onStartActivity(this, intent);
+        for (Listener listener : mListeners) {
+            listener.onStartActivity(this, intent);
         }
     }
 
     private void fireCallDestroyed() {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onCallDestroyed(this);
+        for (Listener listener : mListeners) {
+            listener.onCallDestroyed(this);
         }
     }
 
     private void fireConferenceableCallsChanged() {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onConferenceableCallsChanged(this, mUnmodifiableConferenceableCalls);
+        for (Listener listener : mListeners) {
+            listener.onConferenceableCallsChanged(this, mUnmodifiableConferenceableCalls);
         }
     }
 
diff --git a/telecomm/java/android/telecomm/Connection.java b/telecomm/java/android/telecomm/Connection.java
index 3ecb4cb..78c34a1 100644
--- a/telecomm/java/android/telecomm/Connection.java
+++ b/telecomm/java/android/telecomm/Connection.java
@@ -32,7 +32,7 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Set;
-import java.util.concurrent.CopyOnWriteArraySet;
+import java.util.concurrent.ConcurrentHashMap;
 
 /**
  * Represents a connection to a remote endpoint that carries voice traffic.
@@ -448,7 +448,13 @@
         }
     };
 
-    private final Set<Listener> mListeners = new CopyOnWriteArraySet<>();
+    /**
+     * ConcurrentHashMap constructor params: 8 is initial table size, 0.9f is
+     * load factor before resizing, 1 means we only expect a single thread to
+     * access the map so make only a single shard
+     */
+    private final Set<Listener> mListeners = Collections.newSetFromMap(
+            new ConcurrentHashMap<Listener, Boolean>(8, 0.9f, 1));
     private final List<Connection> mChildConnections = new ArrayList<>();
     private final List<Connection> mUnmodifiableChildConnections =
             Collections.unmodifiableList(mChildConnections);
@@ -587,7 +593,9 @@
      * @hide
      */
     public final Connection removeConnectionListener(Listener l) {
-        mListeners.remove(l);
+        if (l != null) {
+            mListeners.remove(l);
+        }
         return this;
     }
 
@@ -874,13 +882,8 @@
      * Tears down the Connection object.
      */
     public final void destroy() {
-        // It is possible that onDestroy() will trigger the listener to remove itself which will
-        // result in a concurrent modification exception. To counteract this we make a copy of the
-        // listeners and iterate on that.
-        for (Listener l : new ArrayList<>(mListeners)) {
-            if (mListeners.contains(l)) {
-                l.onDestroyed(this);
-            }
+        for (Listener l : mListeners) {
+            l.onDestroyed(this);
         }
     }
 
diff --git a/telecomm/java/android/telecomm/ConnectionServiceAdapter.java b/telecomm/java/android/telecomm/ConnectionServiceAdapter.java
index bfcb5c3..4144b81 100644
--- a/telecomm/java/android/telecomm/ConnectionServiceAdapter.java
+++ b/telecomm/java/android/telecomm/ConnectionServiceAdapter.java
@@ -36,8 +36,13 @@
  * @hide
  */
 final class ConnectionServiceAdapter implements DeathRecipient {
+    /**
+     * ConcurrentHashMap constructor params: 8 is initial table size, 0.9f is
+     * load factor before resizing, 1 means we only expect a single thread to
+     * access the map so make only a single shard
+     */
     private final Set<IConnectionServiceAdapter> mAdapters = Collections.newSetFromMap(
-            new ConcurrentHashMap<IConnectionServiceAdapter, Boolean>(2));
+            new ConcurrentHashMap<IConnectionServiceAdapter, Boolean>(8, 0.9f, 1));
 
     ConnectionServiceAdapter() {
     }
@@ -53,7 +58,7 @@
     }
 
     void removeAdapter(IConnectionServiceAdapter adapter) {
-        if (mAdapters.remove(adapter)) {
+        if (adapter != null && mAdapters.remove(adapter)) {
             adapter.asBinder().unlinkToDeath(this, 0);
         }
     }
diff --git a/telecomm/java/android/telecomm/Phone.java b/telecomm/java/android/telecomm/Phone.java
index 79e777a..03a8676 100644
--- a/telecomm/java/android/telecomm/Phone.java
+++ b/telecomm/java/android/telecomm/Phone.java
@@ -24,6 +24,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.concurrent.CopyOnWriteArrayList;
 
 /**
  * A unified virtual device providing a means of voice (and other) communication on a device.
@@ -89,7 +90,7 @@
 
     private AudioState mAudioState;
 
-    private final List<Listener> mListeners = new ArrayList<>();
+    private final List<Listener> mListeners = new CopyOnWriteArrayList<>();
 
     /** {@hide} */
     Phone(InCallAdapter adapter) {
@@ -171,7 +172,9 @@
      * @param listener A {@code Listener} object.
      */
     public final void removeListener(Listener listener) {
-        mListeners.remove(listener);
+        if (listener != null) {
+            mListeners.remove(listener);
+        }
     }
 
     /**
@@ -236,30 +239,26 @@
     }
 
     private void fireCallAdded(Call call) {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onCallAdded(this, call);
+        for (Listener listener : mListeners) {
+            listener.onCallAdded(this, call);
         }
     }
 
     private void fireCallRemoved(Call call) {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onCallRemoved(this, call);
+        for (Listener listener : mListeners) {
+            listener.onCallRemoved(this, call);
         }
     }
 
     private void fireAudioStateChanged(AudioState audioState) {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onAudioStateChanged(this, audioState);
+        for (Listener listener : mListeners) {
+            listener.onAudioStateChanged(this, audioState);
         }
     }
 
     private void fireBringToForeground(boolean showDialpad) {
-        Listener[] listeners = mListeners.toArray(new Listener[mListeners.size()]);
-        for (int i = 0; i < listeners.length; i++) {
-            listeners[i].onBringToForeground(this, showDialpad);
+        for (Listener listener : mListeners) {
+            listener.onBringToForeground(this, showDialpad);
         }
     }
 
diff --git a/telecomm/java/android/telecomm/RemoteConnection.java b/telecomm/java/android/telecomm/RemoteConnection.java
index d3972d31..f1cee10 100644
--- a/telecomm/java/android/telecomm/RemoteConnection.java
+++ b/telecomm/java/android/telecomm/RemoteConnection.java
@@ -184,8 +184,13 @@
 
     private IConnectionService mConnectionService;
     private final String mConnectionId;
+    /**
+     * ConcurrentHashMap constructor params: 8 is initial table size, 0.9f is
+     * load factor before resizing, 1 means we only expect a single thread to
+     * access the map so make only a single shard
+     */
     private final Set<Listener> mListeners = Collections.newSetFromMap(
-            new ConcurrentHashMap<Listener, Boolean>(2));
+            new ConcurrentHashMap<Listener, Boolean>(8, 0.9f, 1));
     private final Set<RemoteConnection> mConferenceableConnections = new HashSet<>();
 
     private int mState = Connection.STATE_NEW;
@@ -248,7 +253,9 @@
      * @param listener A {@code Listener}.
      */
     public void removeListener(Listener listener) {
-        mListeners.remove(listener);
+        if (listener != null) {
+            mListeners.remove(listener);
+        }
     }
 
     /**
@@ -588,11 +595,10 @@
                 setDisconnected(DisconnectCause.ERROR_UNSPECIFIED, "Connection destroyed.");
             }
 
-            Set<Listener> listeners = new HashSet<Listener>(mListeners);
-            mListeners.clear();
-            for (Listener l : listeners) {
+            for (Listener l : mListeners) {
                 l.onDestroyed(this);
             }
+            mListeners.clear();
 
             mConnected = false;
         }