diff --git a/src/java/com/android/internal/telephony/Phone.java b/src/java/com/android/internal/telephony/Phone.java
index 2e10703..f84dec4 100644
--- a/src/java/com/android/internal/telephony/Phone.java
+++ b/src/java/com/android/internal/telephony/Phone.java
@@ -2284,6 +2284,17 @@
     }
 
     /**
+     * Initiate to add a participant in an IMS call.
+     *
+     * @exception CallStateException operation is not supported.
+     */
+    public void addParticipant(String dialString, Message onComplete) throws CallStateException {
+        // To be overridden by GsmCdmaPhone and ImsPhone.
+        throw new CallStateException("addParticipant :: No-Op base implementation. "
+                + this);
+    }
+
+    /**
      * send burst DTMF tone, it can send the string as single character or multiple character
      * ignore if there is no active call or not valid digits string.
      * Valid digit means only includes characters ISO-LATIN characters 0-9, *, #
diff --git a/src/java/com/android/internal/telephony/imsphone/ImsPhone.java b/src/java/com/android/internal/telephony/imsphone/ImsPhone.java
index 3217f2e..7190d3a 100644
--- a/src/java/com/android/internal/telephony/imsphone/ImsPhone.java
+++ b/src/java/com/android/internal/telephony/imsphone/ImsPhone.java
@@ -581,7 +581,12 @@
 
     @Override
     public void addParticipant(String dialString) throws CallStateException {
-        mCT.addParticipant(dialString);
+        addParticipant(dialString, null);
+    }
+
+    @Override
+    public void addParticipant(String dialString, Message onComplete) throws CallStateException {
+        mCT.addParticipant(dialString, onComplete);
     }
 
     @Override
diff --git a/src/java/com/android/internal/telephony/imsphone/ImsPhoneCallTracker.java b/src/java/com/android/internal/telephony/imsphone/ImsPhoneCallTracker.java
index 58c5ee1..0494a6a 100644
--- a/src/java/com/android/internal/telephony/imsphone/ImsPhoneCallTracker.java
+++ b/src/java/com/android/internal/telephony/imsphone/ImsPhoneCallTracker.java
@@ -221,6 +221,9 @@
     private ImsCall mCallExpectedToResume = null;
     private boolean mAllowEmergencyVideoCalls = false;
 
+    private Object mAddParticipantLock = new Object();
+    private Message mAddPartResp;
+
     //***** Events
 
 
@@ -432,7 +435,9 @@
         return mPendingMO;
     }
 
-    public void addParticipant(String dialString) throws CallStateException {
+    public void
+    addParticipant(String dialString, Message onComplete) throws CallStateException {
+        boolean isSuccess = false;
         if (mForegroundCall != null) {
             ImsCall imsCall = mForegroundCall.getImsCall();
             if (imsCall == null) {
@@ -440,8 +445,12 @@
             } else {
                 ImsCallSession imsCallSession = imsCall.getCallSession();
                 if (imsCallSession != null) {
-                    String[] callees = new String[] { dialString };
-                    imsCallSession.inviteParticipants(callees);
+                    synchronized (mAddParticipantLock) {
+                        mAddPartResp = onComplete;
+                        String[] callees = new String[] { dialString };
+                        imsCallSession.inviteParticipants(callees);
+                        isSuccess = true;
+                    }
                 } else {
                     loge("addParticipant : ImsCallSession does not exist");
                 }
@@ -449,6 +458,23 @@
         } else {
             loge("addParticipant : Foreground call does not exist");
         }
+        if (!isSuccess && onComplete != null) {
+            sendAddParticipantResponse(false, onComplete);
+            mAddPartResp = null;
+        }
+    }
+
+    private void sendAddParticipantResponse(boolean success, Message onComplete) {
+        loge("sendAddParticipantResponse : success = " + success);
+        if (onComplete == null) return;
+
+        Exception ex = null;
+        if (!success) {
+            ex = new Exception("Add participant failed");
+        }
+
+        AsyncResult.forMessage(onComplete, null, ex);
+        onComplete.sendToTarget();
     }
 
     /**
@@ -1685,6 +1711,24 @@
                 conn.updateMultipartyState(isMultiParty);
             }
         }
+
+        public void onCallInviteParticipantsRequestDelivered(ImsCall call) {
+            if (DBG) log("invite participants delivered");
+            synchronized(mAddParticipantLock) {
+                sendAddParticipantResponse(true, mAddPartResp);
+                mAddPartResp = null;
+            }
+        }
+
+        @Override
+        public void onCallInviteParticipantsRequestFailed(ImsCall call,
+                ImsReasonInfo reasonInfo) {
+            if (DBG) log("invite participants failed.");
+            synchronized(mAddParticipantLock) {
+                sendAddParticipantResponse(false, mAddPartResp);
+                mAddPartResp = null;
+            }
+        }
     };
 
     /**
diff --git a/tests/telephonytests/src/com/android/internal/telephony/imsphone/ImsPhoneTest.java b/tests/telephonytests/src/com/android/internal/telephony/imsphone/ImsPhoneTest.java
index f0ca274..0bb3f2b 100644
--- a/tests/telephonytests/src/com/android/internal/telephony/imsphone/ImsPhoneTest.java
+++ b/tests/telephonytests/src/com/android/internal/telephony/imsphone/ImsPhoneTest.java
@@ -385,6 +385,15 @@
 
     @Test
     @SmallTest
+    public void testAddParticipant() throws Exception {
+        String dialString = "1234567890";
+
+        mImsPhoneUT.addParticipant(dialString, null);
+        verify(mImsCT).addParticipant(dialString, null);
+    }
+
+    @Test
+    @SmallTest
     public void testDtmf() {
         // case 1
         doReturn(PhoneConstants.State.IDLE).when(mImsCT).getState();