Change SMS/Voice code delivery priorities.

1) Honor a twilio.international configuration boolean that
   specifies whether to use twilio for international destinations.

2) If a nexmo configuration is specified, and Twilio fails to
   deliver, fall back and attempt delivery again with nexmo.

config/sample.yml

@@ -3,9 +3,12 @@ twilio:
   accountToken:
   number:
   localDomain: # The domain Twilio can call back to.
+  international: # Boolean specifying Twilio for international delivery
 
 # Optional. If specified, Nexmo will be used for non-US SMS and 
-# voice verification.
+# voice verification if twilio.international is false. Otherwise,
+# Nexmo, if specified, Nexmo will only be used as a fallback
+# for failed Twilio deliveries.
 nexmo:
   apiKey:
   apiSecret:

src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java

@@ -16,6 +16,7 @@
  */
 package org.whispersystems.textsecuregcm;
 
+import com.google.common.base.Optional;
 import com.yammer.dropwizard.Service;
 import com.yammer.dropwizard.config.Bootstrap;
 import com.yammer.dropwizard.config.Environment;
@@ -29,6 +30,7 @@ import org.skife.jdbi.v2.DBI;
 import org.whispersystems.textsecuregcm.auth.AccountAuthenticator;
 import org.whispersystems.textsecuregcm.auth.FederatedPeerAuthenticator;
 import org.whispersystems.textsecuregcm.auth.MultiBasicAuthProvider;
+import org.whispersystems.textsecuregcm.configuration.NexmoConfiguration;
 import org.whispersystems.textsecuregcm.controllers.AccountController;
 import org.whispersystems.textsecuregcm.controllers.AttachmentController;
 import org.whispersystems.textsecuregcm.controllers.DirectoryController;
@@ -45,7 +47,9 @@ import org.whispersystems.textsecuregcm.providers.MemcachedClientFactory;
 import org.whispersystems.textsecuregcm.providers.RedisClientFactory;
 import org.whispersystems.textsecuregcm.providers.RedisHealthCheck;
 import org.whispersystems.textsecuregcm.push.PushSender;
-import org.whispersystems.textsecuregcm.sms.SenderFactory;
+import org.whispersystems.textsecuregcm.sms.NexmoSmsSender;
+import org.whispersystems.textsecuregcm.sms.SmsSender;
+import org.whispersystems.textsecuregcm.sms.TwilioSmsSender;
 import org.whispersystems.textsecuregcm.storage.Account;
 import org.whispersystems.textsecuregcm.storage.Accounts;
 import org.whispersystems.textsecuregcm.storage.AccountsManager;
@@ -93,24 +97,26 @@ public class WhisperServerService extends Service<WhisperServerConfiguration> {
     MemcachedClient memcachedClient = new MemcachedClientFactory(config.getMemcacheConfiguration()).getClient();
     JedisPool       redisClient     = new RedisClientFactory(config.getRedisConfiguration()).getRedisClientPool();
 
-    DirectoryManager       directory              = new DirectoryManager(redisClient);
+    DirectoryManager         directory              = new DirectoryManager(redisClient);
-    PendingAccountsManager pendingAccountsManager = new PendingAccountsManager(pendingAccounts, memcachedClient);
+    PendingAccountsManager   pendingAccountsManager = new PendingAccountsManager(pendingAccounts, memcachedClient);
-    AccountsManager        accountsManager        = new AccountsManager(accounts, directory, memcachedClient);
+    AccountsManager          accountsManager        = new AccountsManager(accounts, directory, memcachedClient);
-    AccountAuthenticator   accountAuthenticator   = new AccountAuthenticator(accountsManager);
+    AccountAuthenticator     accountAuthenticator   = new AccountAuthenticator(accountsManager                     );
-    FederatedClientManager federatedClientManager = new FederatedClientManager(config.getFederationConfiguration());
+    FederatedClientManager   federatedClientManager = new FederatedClientManager(config.getFederationConfiguration());
-    RateLimiters           rateLimiters           = new RateLimiters(config.getLimitsConfiguration(), memcachedClient);
+    RateLimiters             rateLimiters           = new RateLimiters(config.getLimitsConfiguration(), memcachedClient);
-    SenderFactory          senderFactory          = new SenderFactory(config.getTwilioConfiguration(), config.getNexmoConfiguration());
+    TwilioSmsSender          twilioSmsSender        = new TwilioSmsSender(config.getTwilioConfiguration());
-    UrlSigner              urlSigner              = new UrlSigner(config.getS3Configuration());
+    Optional<NexmoSmsSender> nexmoSmsSender         = initializeNexmoSmsSender(config.getNexmoConfiguration());
-    PushSender             pushSender             = new PushSender(config.getGcmConfiguration(),
+    SmsSender                smsSender              = new SmsSender(twilioSmsSender, nexmoSmsSender, config.getTwilioConfiguration().isInternational());
-                                                                   config.getApnConfiguration(),
+    UrlSigner                urlSigner              = new UrlSigner(config.getS3Configuration());
-                                                                   accountsManager, directory);
+    PushSender               pushSender             = new PushSender(config.getGcmConfiguration(),
+                                                                     config.getApnConfiguration(),
+                                                                     accountsManager, directory);
 
     environment.addProvider(new MultiBasicAuthProvider<>(new FederatedPeerAuthenticator(config.getFederationConfiguration()),
                                                          FederatedPeer.class,
                                                          accountAuthenticator,
                                                          Account.class, "WhisperServer"));
 
-    environment.addResource(new AccountController(pendingAccountsManager, accountsManager, rateLimiters, senderFactory));
+    environment.addResource(new AccountController(pendingAccountsManager, accountsManager, rateLimiters, smsSender));
     environment.addResource(new DirectoryController(rateLimiters, directory));
     environment.addResource(new AttachmentController(rateLimiters, federatedClientManager, urlSigner));
     environment.addResource(new KeysController(rateLimiters, keys, federatedClientManager));
@@ -133,6 +139,14 @@ public class WhisperServerService extends Service<WhisperServerConfiguration> {
     }
   }
 
+  private Optional<NexmoSmsSender> initializeNexmoSmsSender(NexmoConfiguration configuration) {
+    if (configuration == null) {
+      return Optional.absent();
+    } else {
+      return Optional.of(new NexmoSmsSender(configuration));
+    }
+  }
+
   public static void main(String[] args) throws Exception {
     new WhisperServerService().run(args);
   }

src/main/java/org/whispersystems/textsecuregcm/configuration/TwilioConfiguration.java

@@ -37,6 +37,9 @@ public class TwilioConfiguration {
   @JsonProperty
   private String localDomain;
 
+  @JsonProperty
+  private boolean international;
+
   public String getAccountId() {
     return accountId;
   }
@@ -52,4 +55,8 @@ public class TwilioConfiguration {
   public String getLocalDomain() {
     return localDomain;
   }
+
+  public boolean isInternational() {
+    return international;
+  }
 }

src/main/java/org/whispersystems/textsecuregcm/controllers/AccountController.java

@@ -28,7 +28,7 @@ import org.whispersystems.textsecuregcm.entities.AccountAttributes;
 import org.whispersystems.textsecuregcm.entities.ApnRegistrationId;
 import org.whispersystems.textsecuregcm.entities.GcmRegistrationId;
 import org.whispersystems.textsecuregcm.limits.RateLimiters;
-import org.whispersystems.textsecuregcm.sms.SenderFactory;
+import org.whispersystems.textsecuregcm.sms.SmsSender;
 import org.whispersystems.textsecuregcm.sms.TwilioSmsSender;
 import org.whispersystems.textsecuregcm.storage.Account;
 import org.whispersystems.textsecuregcm.storage.AccountsManager;
@@ -61,17 +61,17 @@ public class AccountController {
   private final PendingAccountsManager pendingAccounts;
   private final AccountsManager        accounts;
   private final RateLimiters           rateLimiters;
-  private final SenderFactory          senderFactory;
+  private final SmsSender              smsSender;
 
   public AccountController(PendingAccountsManager pendingAccounts,
                            AccountsManager accounts,
                            RateLimiters rateLimiters,
-                           SenderFactory smsSenderFactory)
+                           SmsSender smsSenderFactory)
   {
     this.pendingAccounts = pendingAccounts;
     this.accounts        = accounts;
     this.rateLimiters    = rateLimiters;
-    this.senderFactory   = smsSenderFactory;
+    this.smsSender       = smsSenderFactory;
   }
 
   @Timed
@@ -101,9 +101,9 @@ public class AccountController {
     pendingAccounts.store(number, verificationCode.getVerificationCode());
 
     if (transport.equals("sms")) {
-      senderFactory.getSmsSender(number).deliverSmsVerification(number, verificationCode.getVerificationCodeDisplay());
+      smsSender.deliverSmsVerification(number, verificationCode.getVerificationCodeDisplay());
     } else if (transport.equals("voice")) {
-      senderFactory.getVoxSender(number).deliverVoxVerification(number, verificationCode.getVerificationCodeSpeech());
+      smsSender.deliverVoxVerification(number, verificationCode.getVerificationCodeSpeech());
     }
 
     return Response.ok().build();
@@ -190,8 +190,7 @@ public class AccountController {
   @Produces(MediaType.APPLICATION_XML)
   public Response getTwiml(@PathParam("code") String encodedVerificationText) {
     return Response.ok().entity(String.format(TwilioSmsSender.SAY_TWIML,
-                                              SenderFactory.VoxSender.VERIFICATION_TEXT +
+                                              encodedVerificationText)).build();
-                                                  encodedVerificationText)).build();
   }
 
   private VerificationCode generateVerificationCode() {

src/main/java/org/whispersystems/textsecuregcm/sms/NexmoSmsSender.java

@@ -30,10 +30,7 @@ import java.net.URLConnection;
 import java.net.URLEncoder;
 import java.util.concurrent.TimeUnit;
 
-import org.whispersystems.textsecuregcm.sms.SenderFactory.VoxSender;
+public class NexmoSmsSender {
-import org.whispersystems.textsecuregcm.sms.SenderFactory.SmsSender;
-
-public class NexmoSmsSender implements SmsSender, VoxSender {
 
   private final Meter  smsMeter = Metrics.newMeter(NexmoSmsSender.class, "sms", "delivered", TimeUnit.MINUTES);
   private final Meter  voxMeter = Metrics.newMeter(NexmoSmsSender.class, "vox", "delivered", TimeUnit.MINUTES);
@@ -55,10 +52,9 @@ public class NexmoSmsSender implements SmsSender, VoxSender {
     this.number    = config.getNumber();
   }
 
-  @Override
   public void deliverSmsVerification(String destination, String verificationCode) throws IOException {
     URL url = new URL(String.format(NEXMO_SMS_URL, apiKey, apiSecret, number, destination,
-                                    URLEncoder.encode(SmsSender.VERIFICATION_TEXT + verificationCode, "UTF-8")));
+                                    URLEncoder.encode(SmsSender.SMS_VERIFICATION_TEXT + verificationCode, "UTF-8")));
 
     URLConnection connection = url.openConnection();
     connection.setDoInput(true);
@@ -70,10 +66,9 @@ public class NexmoSmsSender implements SmsSender, VoxSender {
     smsMeter.mark();
   }
 
-  @Override
   public void deliverVoxVerification(String destination, String message) throws IOException {
     URL url = new URL(String.format(NEXMO_VOX_URL, apiKey, apiSecret, destination,
-                                    URLEncoder.encode(VoxSender.VERIFICATION_TEXT + message, "UTF-8")));
+                                    URLEncoder.encode(SmsSender.VOX_VERIFICATION_TEXT + message, "UTF-8")));
 
     URLConnection connection = url.openConnection();
     connection.setDoInput(true);

src/main/java/org/whispersystems/textsecuregcm/sms/SenderFactory.java

@@ -1,70 +0,0 @@
-/**
- * Copyright (C) 2013 Open WhisperSystems
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU Affero General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU Affero General Public License for more details.
- *
- * You should have received a copy of the GNU Affero General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- */
-package org.whispersystems.textsecuregcm.sms;
-
-
-import com.google.common.base.Optional;
-import org.whispersystems.textsecuregcm.configuration.NexmoConfiguration;
-import org.whispersystems.textsecuregcm.configuration.TwilioConfiguration;
-
-import java.io.IOException;
-
-public class SenderFactory {
-
-  private final TwilioSmsSender          twilioSender;
-  private final Optional<NexmoSmsSender> nexmoSender;
-
-  public SenderFactory(TwilioConfiguration twilioConfig, NexmoConfiguration nexmoConfig) {
-    this.twilioSender = new TwilioSmsSender(twilioConfig);
-
-    if (nexmoConfig != null) {
-      this.nexmoSender = Optional.of(new NexmoSmsSender(nexmoConfig));
-    } else {
-      this.nexmoSender = Optional.absent();
-    }
-  }
-
-  public SmsSender getSmsSender(String number) {
-    if (nexmoSender.isPresent() && !isTwilioDestination(number)) {
-      return nexmoSender.get();
-    } else {
-      return twilioSender;
-    }
-  }
-
-  public VoxSender getVoxSender(String number) {
-    if (nexmoSender.isPresent()) {
-      return nexmoSender.get();
-    } else {
-      return twilioSender;
-    }
-  }
-
-  private boolean isTwilioDestination(String number) {
-    return number.length() == 12 && number.startsWith("+1");
-  }
-
-  public interface SmsSender {
-    public static final String VERIFICATION_TEXT = "Your TextSecure verification code: ";
-    public void deliverSmsVerification(String destination, String verificationCode) throws IOException;
-  }
-
-  public interface VoxSender {
-    public static final String VERIFICATION_TEXT = "Your TextSecure verification code is: ";
-    public void deliverVoxVerification(String destination, String verificationCode) throws IOException;
-  }
-}

src/main/java/org/whispersystems/textsecuregcm/sms/SmsSender.java

@@ -0,0 +1,84 @@
+/**
+ * Copyright (C) 2013 Open WhisperSystems
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.whispersystems.textsecuregcm.sms;
+
+
+import com.google.common.base.Optional;
+import com.twilio.sdk.TwilioRestException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+
+public class SmsSender {
+
+  static final String SMS_VERIFICATION_TEXT = "Your TextSecure verification code: ";
+  static final String VOX_VERIFICATION_TEXT = "Your TextSecure verification code is: ";
+
+  private final Logger logger = LoggerFactory.getLogger(SmsSender.class);
+
+  private final TwilioSmsSender          twilioSender;
+  private final Optional<NexmoSmsSender> nexmoSender;
+  private final boolean                  isTwilioInternational;
+
+  public SmsSender(TwilioSmsSender twilioSender,
+                   Optional<NexmoSmsSender> nexmoSender,
+                   boolean isTwilioInternational)
+  {
+    this.isTwilioInternational = isTwilioInternational;
+    this.twilioSender          = twilioSender;
+    this.nexmoSender           = nexmoSender;
+  }
+
+  public void deliverSmsVerification(String destination, String verificationCode)
+      throws IOException
+  {
+    if (!isTwilioDestination(destination) && nexmoSender.isPresent()) {
+      nexmoSender.get().deliverSmsVerification(destination, verificationCode);
+    } else {
+      try {
+        twilioSender.deliverSmsVerification(destination, verificationCode);
+      } catch (TwilioRestException e) {
+        logger.info("Twilio SMS Fallback", e);
+        if (nexmoSender.isPresent()) {
+          nexmoSender.get().deliverSmsVerification(destination, verificationCode);
+        }
+      }
+    }
+  }
+
+  public void deliverVoxVerification(String destination, String verificationCode)
+      throws IOException
+  {
+    if (!isTwilioDestination(destination) && nexmoSender.isPresent()) {
+      nexmoSender.get().deliverVoxVerification(destination, verificationCode);
+    } else {
+      try {
+        twilioSender.deliverVoxVerification(destination, verificationCode);
+      } catch (TwilioRestException e) {
+        logger.info("Twilio Vox Fallback", e);
+        if (nexmoSender.isPresent()) {
+          nexmoSender.get().deliverVoxVerification(destination, verificationCode);
+        }
+      }
+    }
+  }
+
+  private boolean isTwilioDestination(String number) {
+    return isTwilioInternational || number.length() == 12 && number.startsWith("+1");
+  }
+}

src/main/java/org/whispersystems/textsecuregcm/sms/TwilioSmsSender.java

@@ -33,11 +33,11 @@ import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 
-public class TwilioSmsSender implements SenderFactory.SmsSender, SenderFactory.VoxSender {
+public class TwilioSmsSender {
 
   public static final String SAY_TWIML = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
                                          "<Response>\n" +
-                                         "    <Say voice=\"woman\" language=\"en\">%s</Say>\n" +
+                                         "    <Say voice=\"woman\" language=\"en\">" + SmsSender.VOX_VERIFICATION_TEXT + "%s</Say>\n" +
                                          "</Response>";
 
   private final Meter smsMeter = Metrics.newMeter(TwilioSmsSender.class, "sms", "delivered", TimeUnit.MINUTES);
@@ -55,37 +55,39 @@ public class TwilioSmsSender implements SenderFactory.SmsSender, SenderFactory.V
     this.localDomain  = config.getLocalDomain();
   }
 
-  @Override
   public void deliverSmsVerification(String destination, String verificationCode)
-      throws IOException
+      throws IOException, TwilioRestException
   {
+    TwilioRestClient    client         = new TwilioRestClient(accountId, accountToken);
+    MessageFactory      messageFactory = client.getAccount().getMessageFactory();
+    List<NameValuePair> messageParams  = new LinkedList<>();
+    messageParams.add(new BasicNameValuePair("To", destination));
+    messageParams.add(new BasicNameValuePair("From", number));
+    messageParams.add(new BasicNameValuePair("Body", SmsSender.SMS_VERIFICATION_TEXT + verificationCode));
+
     try {
-      TwilioRestClient    client         = new TwilioRestClient(accountId, accountToken);
-      MessageFactory      messageFactory = client.getAccount().getMessageFactory();
-      List<NameValuePair> messageParams  = new LinkedList<>();
-      messageParams.add(new BasicNameValuePair("To", destination));
-      messageParams.add(new BasicNameValuePair("From", number));
-      messageParams.add(new BasicNameValuePair("Body", SenderFactory.SmsSender.VERIFICATION_TEXT + verificationCode));
       messageFactory.create(messageParams);
-    } catch (TwilioRestException e) {
+    } catch (RuntimeException damnYouTwilio) {
-      throw new IOException(e);
+      throw new IOException(damnYouTwilio);
     }
 
     smsMeter.mark();
   }
 
-  @Override
+  public void deliverVoxVerification(String destination, String verificationCode)
-  public void deliverVoxVerification(String destination, String verificationCode) throws IOException {
+      throws IOException, TwilioRestException
+  {
+    TwilioRestClient    client      = new TwilioRestClient(accountId, accountToken);
+    CallFactory         callFactory = client.getAccount().getCallFactory();
+    Map<String, String> callParams  = new HashMap<>();
+    callParams.put("To", destination);
+    callParams.put("From", number);
+    callParams.put("Url", "https://" + localDomain + "/v1/accounts/voice/twiml/" + verificationCode);
+
     try {
-      TwilioRestClient    client      = new TwilioRestClient(accountId, accountToken);
-      CallFactory         callFactory = client.getAccount().getCallFactory();
-      Map<String, String> callParams  = new HashMap<>();
-      callParams.put("To", destination);
-      callParams.put("From", number);
-      callParams.put("Url", "https://" + localDomain + "/v1/accounts/voice/twiml/" + verificationCode);
       callFactory.create(callParams);
-    } catch (TwilioRestException e) {
+    } catch (RuntimeException damnYouTwilio) {
-      throw new IOException(e);
+      throw new IOException(damnYouTwilio);
     }
 
     voxMeter.mark();

src/test/org/whispersystems/textsecuregcm/tests/controllers/AccountControllerTest.java

@@ -8,8 +8,7 @@ import org.whispersystems.textsecuregcm.controllers.AccountController;
 import org.whispersystems.textsecuregcm.entities.AccountAttributes;
 import org.whispersystems.textsecuregcm.limits.RateLimiter;
 import org.whispersystems.textsecuregcm.limits.RateLimiters;
-import org.whispersystems.textsecuregcm.sms.SenderFactory;
+import org.whispersystems.textsecuregcm.sms.SmsSender;
-import org.whispersystems.textsecuregcm.sms.TwilioSmsSender;
 import org.whispersystems.textsecuregcm.storage.Account;
 import org.whispersystems.textsecuregcm.storage.AccountsManager;
 import org.whispersystems.textsecuregcm.storage.PendingAccountsManager;
@@ -29,8 +28,7 @@ public class AccountControllerTest extends ResourceTest {
   private AccountsManager        accountsManager        = mock(AccountsManager.class       );
   private RateLimiters           rateLimiters           = mock(RateLimiters.class          );
   private RateLimiter            rateLimiter            = mock(RateLimiter.class           );
-  private TwilioSmsSender        twilioSmsSender        = mock(TwilioSmsSender.class       );
+  private SmsSender              smsSender              = mock(SmsSender.class             );
-  private SenderFactory          senderFactory          = mock(SenderFactory.class         );
 
   @Override
   protected void setUpResources() throws Exception {
@@ -41,12 +39,11 @@ public class AccountControllerTest extends ResourceTest {
     when(rateLimiters.getVerifyLimiter()).thenReturn(rateLimiter);
 
     when(pendingAccountsManager.getCodeForNumber(SENDER)).thenReturn(Optional.of("1234"));
-    when(senderFactory.getSmsSender(SENDER)).thenReturn(twilioSmsSender);
 
     addResource(new AccountController(pendingAccountsManager,
                                       accountsManager,
                                       rateLimiters,
-                                      senderFactory));
+                                      smsSender));
   }
 
   @Test
@@ -57,7 +54,7 @@ public class AccountControllerTest extends ResourceTest {
 
     assertThat(response.getStatus()).isEqualTo(200);
 
-    verify(twilioSmsSender).deliverSmsVerification(eq(SENDER), anyString());
+    verify(smsSender).deliverSmsVerification(eq(SENDER), anyString());
   }
 
   @Test

src/test/org/whispersystems/textsecuregcm/tests/sms/DeliveryPreferenceTest.java

@@ -0,0 +1,36 @@
+package org.whispersystems.textsecuregcm.tests.sms;
+
+import com.google.common.base.Optional;
+import com.twilio.sdk.TwilioRestException;
+import junit.framework.TestCase;
+import org.whispersystems.textsecuregcm.sms.NexmoSmsSender;
+import org.whispersystems.textsecuregcm.sms.SmsSender;
+import org.whispersystems.textsecuregcm.sms.TwilioSmsSender;
+
+import java.io.IOException;
+
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoMoreInteractions;
+
+public class DeliveryPreferenceTest extends TestCase {
+
+  private TwilioSmsSender twilioSender = mock(TwilioSmsSender.class);
+  private NexmoSmsSender  nexmoSender  = mock(NexmoSmsSender.class);
+
+  public void testInternationalPreferenceOff() throws IOException, TwilioRestException {
+    SmsSender smsSender = new SmsSender(twilioSender, Optional.of(nexmoSender), false);
+
+    smsSender.deliverSmsVerification("+441112223333", "123-456");
+    verify(nexmoSender).deliverSmsVerification("+441112223333", "123-456");
+    verifyNoMoreInteractions(twilioSender);
+  }
+
+  public void testInternationalPreferenceOn() throws IOException, TwilioRestException {
+    SmsSender smsSender = new SmsSender(twilioSender, Optional.of(nexmoSender), true);
+
+    smsSender.deliverSmsVerification("+441112223333", "123-456");
+    verify(twilioSender).deliverSmsVerification("+441112223333", "123-456");
+    verifyNoMoreInteractions(nexmoSender);
+  }
+}

src/test/org/whispersystems/textsecuregcm/tests/sms/TwilioFallbackTest.java

@@ -0,0 +1,43 @@
+package org.whispersystems.textsecuregcm.tests.sms;
+
+import com.google.common.base.Optional;
+import com.twilio.sdk.TwilioRestException;
+import junit.framework.TestCase;
+import org.whispersystems.textsecuregcm.sms.NexmoSmsSender;
+import org.whispersystems.textsecuregcm.sms.SmsSender;
+import org.whispersystems.textsecuregcm.sms.TwilioSmsSender;
+
+import java.io.IOException;
+
+import static org.mockito.Matchers.anyString;
+import static org.mockito.Mockito.*;
+
+public class TwilioFallbackTest extends TestCase {
+
+  private NexmoSmsSender  nexmoSender  = mock(NexmoSmsSender.class );
+  private TwilioSmsSender twilioSender = mock(TwilioSmsSender.class);
+
+  @Override
+  protected void setUp() throws IOException, TwilioRestException {
+    doThrow(new TwilioRestException("foo", 404)).when(twilioSender).deliverSmsVerification(anyString(), anyString());
+    doThrow(new TwilioRestException("bar", 405)).when(twilioSender).deliverVoxVerification(anyString(), anyString());
+  }
+
+  public void testNexmoSmsFallback() throws IOException, TwilioRestException {
+    SmsSender smsSender = new SmsSender(twilioSender, Optional.of(nexmoSender), true);
+    smsSender.deliverSmsVerification("+442223334444", "123-456");
+
+    verify(nexmoSender).deliverSmsVerification("+442223334444", "123-456");
+    verify(twilioSender).deliverSmsVerification("+442223334444", "123-456");
+  }
+
+  public void testNexmoVoxFallback() throws IOException, TwilioRestException {
+    SmsSender smsSender = new SmsSender(twilioSender, Optional.of(nexmoSender), true);
+    smsSender.deliverVoxVerification("+442223334444", "123-456");
+
+    verify(nexmoSender).deliverVoxVerification("+442223334444", "123-456");
+    verify(twilioSender).deliverVoxVerification("+442223334444", "123-456");
+  }
+
+
+}