Forward your voicemail to Slack with Twilio

This post expands on the previous one I wrote on this topic. Please refer back to Virtual support phone number with Twilio if you're not familiar with Twilio.

Following up from last time. We have voice-enabled phone number +420999999999. Now We'll setup call forwarding and voicemail for this number.

Twilio Functions

Functions are a way to run your logic directly on Twilio servers. We'll use them to construct TwiML response and then to send a message to Slack.

Recording voicemail message

Runtime > Functions is the place where we can manage our Functions.

Create a new function called Record message and paste following code. Replace YOUR_RUNTIME_DOMAIN with your Runtime Domain from Runtime Overview page.

exports.handler = function (context, event, callback) {
  let twiml = new Twilio.twiml.VoiceResponse()

  // Use <dial> to forward the call to my phone
  const dial = twiml.dial({
    callerId: '+420999999999',

  // Use <say> to give the caller some instructions
    "We're not available right now. Please leave a message after the beep."

  // Use <record> to record the caller's message
  twiml.record({ action: 'https://YOUR_RUNTIME_DOMAIN/slack' })

  // End the call with <hangup>

  // return the TwiML
  callback(null, twiml)

You probably noticed that record command is pointing to /slack URL. This will be another function. But before we can create it we need to add new npm package to our Runtime > Functions > Configure. The package is called axios and will help us with making HTTP request to Slack.

There's one more thing before we can get to the function and that is Slack Webhook URL. Luckily you can get one by visiting Slack App Directory. After that, we'll have everything we need to create a Function.

var axios = require('axios')

exports.handler = function (context, event, callback) {
    .post('', {
      text: `You have received a message from ${event.From}.\nTo listen to this message, please visit this URL:${event.RecordingUrl}.mp3`,
    .then(function (response) {
      callback(null, 'OK')
    .catch(function (error) {
      callback(null, 'FAIL')

This Function takes the phone number of the caller and recording URL. Then POSTs a message to Slack. Now you'll get a message when somebody leaves you a message.