MainActivity.java

// Construct a request for phone numbers and show the picker
private void requestHint() {
    HintRequest hintRequest = new HintRequest.Builder()
           .setPhoneNumberIdentifierSupported(true)
           .build();
GoogleApiClient apiClient= new GoogleApiClient.Builder(this)
        .addConnectionCallbacks(this)  // implement the callbacks
        .enableAutoManage(this, this)
        .addApi(Auth.CREDENTIALS_API)
        .build();
    PendingIntent intent = Auth.CredentialsApi.getHintPickerIntent(
            apiClient, hintRequest);
    startIntentSenderForResult(intent.getIntentSender(),
            RESOLVE_HINT, null, 0, 0, 0);
}