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Receive an incoming phone call

When someone calls your Twilio number, Twilio can invoke a webhook that you've created to determine how to respond using TwiML. On this page, we will be providing some examples of Functions that can serve as the webhook of your Twilio number.

A Function that responds to webhook requests will receive details about the incoming phone call as properties on the event parameter. These include the phone number of the caller (event.From), the phone number of the recipient (event.To), and other relevant data such as geographic metadata about the phone numbers involved. You can view a full list of potential values at Twilio's request to your application.

Once a Function has been invoked on an incoming phone call, any number of actions can be taken. Below are some examples to inspire what you will build.

Create and host a Function

In order to run any of the following examples, you will first need to create a Function into which you can paste the example code. You can create a Function using the Twilio Console or the Serverless Toolkit as explained below:

If you prefer a UI-driven approach, creating and deploying a Function can be done entirely using the Twilio Console and the following steps:

  1. Log in to the Twilio Console and navigate to the Functions tab. If you need an account, you can sign up for a free Twilio account here!
  2. Functions are contained within Services. Create a Service by clicking the Create Service button and providing a name such as test-function.
  3. Once you've been redirected to the new Service, click the Add + button and select Add Function from the dropdown.
  4. This will create a new Protected Function for you with the option to rename it. The name of the file will be path it is accessed from.
  5. Copy any one of the example code snippets from this page that you want to experiment with, and paste the code into your newly created Function. You can quickly switch examples by using the dropdown menu of the code rail.
  6. Click Save to save your Function's contents.
  7. Click Deploy All to build and deploy the Function. After a short delay, your Function will be accesible from:
    https://<service-name>-<random-characters>-<optional-domain-suffix>.twil.io/<function-path>​
    For example: test-function-3548.twil.io/hello-world.

The Serverless Toolkit enables you with local development, project deployment, and other functionality via the Twilio CLI. To get up and running with these examples using Serverless Toolkit, follow this process:

  1. From the CLI, run twilio serverless:init <your-service-name> --empty to bootstrap your local environment.
  2. Navigate into your new project directory using cd <your-service-name>
  3. In the /functions directory, create a new JavaScript file that is named respective to the purpose of the Function. For example, sms-reply.protected.js for a Protected Function intended to handle incoming SMS.
  4. Populate the file using the code example of your choice and save.
    Note A Function can only export a single handler. You will want to create separate files if you want to run and/or deploy multiple examples at once.

Once your Function(s) code is written and saved, you can test it either by running it locally (and optionally tunneling requests to it via a tool like ngrok), or by deploying the Function and executing against the deployed url(s).

Run your Function in local development

Run twilio serverless:start from your CLI to start the project locally. The Function(s) in your project will be accesible from http://localhost:3000/sms-reply

  • If you want to test a Function as a Twilio webhook, run:
    twilio phone-numbers:update <your Twilio phone number> --sms-url "http://localhost:3000/sms-reply"​
    This will automatically generate an ngrok tunnel from Twilio to your locally running Function, so you can start sending texts to it. You can apply the same process but with the voice-url flag instead if you want to test with Twilio Voice.
  • If your code does not connect to Twilio Voice/Messages as a webhook, you can start your dev server and start an ngrok tunnel in the same command with the ngrok flag. For example: twilio serverless:start --ngrok=""

Deploy your Function

To deploy your Function and have access to live url(s), run twilio serverless:deploy from your CLI. This will deploy your Function(s) to Twilio under a development environment by default, where they can be accessed from:

https://<service-name>-<random-characters>-dev.twil.io/<function-path>

For example: https://incoming-sms-examples-3421-dev.twil.io/sms-reply

Your Function is now ready to be invoked by HTTP requests, set as the webhook of a Twilio phone number, invoked by a Twilio Studio Run Function Widget, and more!

Set a Function as a webhook

In order for your Function to react to incoming SMS and/or voice calls, it must be set as a webhook for your Twilio number. There are a variety of methods to set a Function as a webhook, as detailed below:

You can use the Twilio Console UI as a straigforward way of connecting your Function as a webhook:

  1. Log in to the Twilio Console's Phone Numbers page.
  2. Click on the phone number you'd like to have connected to your Function.
  3. If you want the Function to respond to incoming SMS, find the A Message Comes In option under Messaging. If you want the Function to respond to Voice, find the A Call Comes In option under Voice & Fax.
  4. Select Function from the A Message Comes In or A Call Comes In dropdown.
  5. Select the Service that you are using, then the Environment (this will default to ui unless you have created custom domains), and finally Function Path of your Function from the respective dropdown menus.
    Connect a Function as a Messaging webhook using the Function dropdowns
    • Alternatively, you could select Webhook instead of Function, and directly paste in the full URL of the Function.
      Setting a Function as a Messaging webhook using the webhook dropdown option
  6. Click the Save button.

You can also use the Twilio CLI to assign the Function as the webhook of you phone number. You will need a few prerequisites:

  • Twilio CLI installed and executable from your terminal.
  • Either the E.164 formatted value of your Twilio phone number (+1234567890), or its SID (PNXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX).
  • The full URL of your Function (https://test-1337.twil.io/my-test-function)

Once you have the CLI installed and the necessary information, run the following to connect the Function to respond to incoming SMS:

twilio phone-numbers:update +1234567890 --sms-url https://test-1337.twil.io/my-test-function

If you prefer to have the Function respond to incoming calls instead, run:

twilio phone-numbers:update +1234567890 --voice-url https://test-1337.twil.io/my-test-function

You may also use the SID of your Twilio phone number instead of the E.164 formatted phone number:

twilio phone-numbers:update PNXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX --sms-url https://test-1337.twil.io/my-test-function

You can also use any of the avilable Twilio SDKs to assign the Function as the webhook of you phone number. You will need a few prerequisites:

  • A local development environment for your language of choice and the associated Twilio SDK installed.
  • The SID (PNXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX) of your Twilio phone number.
  • The full URL of your Function (https://test-1337.twil.io/my-test-function).

In JavaScript for example, you could execute the following code to assign the SMS webhook of your Twilio phone number. The same logic would apply for assigining to a voice webhook, except that the modified property instead would be voiceUrl:

// Download the helper library from https://www.twilio.com/docs/node/install
// Find your Account SID and Auth Token at twilio.com/console
// and set the environment variables. See http://twil.io/secure
const accountSid = process.env.TWILIO_ACCOUNT_SID;
const authToken = process.env.TWILIO_AUTH_TOKEN;
const client = require('twilio')(accountSid, authToken);

client
  .incomingPhoneNumbers('PNXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX')
  .update({ smsUrl: 'https://test-1337.twil.io/my-test-function' })
  .then((phoneNumber) => console.log(phoneNumber.smsUrl));

Respond with a static message

For the most basic possible example, one can reply to the incoming phone call with a hardcoded message. To do so, you can create a new VoiceResponse and declare the intended message contents using the say method. Once your voice content has been set, you can return the generated TwiML by passing it to the callback function as shown and signaling a successful end to the function.

        
        
        

        Respond dynamically to an incoming phone call

        Because information about the incoming phone call is accessible from event object, it's also possible to tailor the response to the call based on that data. For example, you could respond with the city of the caller's phone number, or the number itself. The voice used to respond can also be modified, and pre-recorded audio can be used and/or added as well.

        Read the in-depth <Say> documentation for more details about how to configure your response.

              
              
              

              Forward an incoming phone call

              Another common use case is call forwarding. This could be handy in a situation where perhaps you don't want to share your real number while selling an item online, or as part of an IVR tree.

              In this example, the Function will accept an incoming phone call and generate a new TwiML response that both notifies the user of the call forwarding and initiates a transfer of the call to the new number.

              Read the in-depth <Dial> documentation for more details about connecting calls to other parties.

                    
                    
                    

                    In this example, the number for call forwarding is hardcoded as a string in the Function for convenience. For a more secure approach, consider setting NEW_NUMBER as an Environment Variable in the Functions UI instead. It could then be referenced in your code as context.NEW_NUMBER, as shown in the following example.

                          
                          
                          
                          Use environment variables to store sensitive values

                          Forward an incoming phone call

                          Use environment variables to store sensitive values

                          Record an incoming phone call

                          Another common use case would be recording the caller's voice as an audio recording which can be retrieved later. Optionally, you can generate text transcriptions of recorded calls by setting the transcribe attribute of <Record> to true.

                          Read the in-depth <Record> documentation for more details about recording and/or transcribing calls.

                                
                                
                                
                                      
                                      
                                      
                                      Use extra options to configure your recording

                                      Record and transcribe an incoming phone call

                                      Use extra options to configure your recording

                                      Creating a moderated conference call

                                      For something more exciting, Functions can also power conference calls. In this example, a "moderator" phone number of your choice will have control of the call in a couple of ways:

                                      • startConferenceOnEnter will keep all other callers on hold until the moderator joins
                                      • endConferenceOnExit will cause Twilio to end the call for everyone as soon as the moderator leaves

                                      Incoming calls will be checked based on the incoming event.From value. If it matches the moderator's phone number, the call will begin and then end once the moderator leaves. Any other phone number will join normally and have no effect on the call's beginning or end.

                                      Read the in-depth <Conference> documentation to learn more details.

                                            
                                            
                                            
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