by netguru


Callio Logo


Callio is a simple app that allows you to answer phone calls in the web browser using Twilio programmable voice service and Slack notifications. It's, more or less, working in the following scenario:

  1. Someone is calling you
  2. Callio is posting a notification on your Slack channel with a link to the web browser client where you can answer the call
  3. You click the link included in Slack notification
  4. When you click the call button in the browser, another notification is posted on your Slack to let the rest of your team know that somebody has already answered the call
  5. Call is performed and recorded
  6. When one of the sides finishes the call, Slack is notifying about that fact and the line is ready to use again

When your line is busy, one who is trying to reach your number can leave you a message. You're of course notified about this fact. Recorded message is available through the link posted on your Slack channel as soon as it's processed on Twilio server.

This app may be useful when:

  • you don't want to care about a physical phone in your office, just a web browser, no additional devices needed
  • you have problems with clients that can't reach your number - thanks to Twilio you can pick a number from dozens of countries
  • you're tired of being sticked to your chair - anyone on your Slack channel can answer the call
  • you want to have a full history of your phone calls with a recorded copy of each one. If you missed something, you still have a note on Slack that somebody was trying to reach you
  • you work remotely - you can still act as an office staff member by answering the calls through the Internet from home

How does it work?

Callio is an extremely lightweight app. It uses Sinatra to communicate with Slack and Twilio APIs, simple web client with some JavaScript to handle the voice calls in the browser and a few webhooks to make it all running smoothly.

Setup, requirements, dependencies

What do you need to start using Callio

Twilio account with number

To start using Callio you have to sign up to Twilio and pick up a number you want to use. It's free and provides full functionality for testing purposes, there's only a short message that you're running a trial account.

Twilio incoming connection webhook

After registering on Twilio and picking up a number, you have to configure your first webhook. To do that, please paste the address of your Callio app under Phone numbers -> Configure -> Voice -> A call comes in.

Twilio webhook for connection finished

In the same place you're pasting the Callio incoming call webhook you can type in the address of the endpoint for notifying users that the call is finished. It's under the call status changes input field.

Twilio Application

When you're done with the number, go to Programmable voice -> Tools -> TwiML apps and create an application. In a few seconds your Twilio app will be ready (we'll need its SID later), then you can configure a webhook there to handle the voice calls by simply typing the address of your Callio app into Voice's requested URL. By default, Callio uses the following URL's to run:

  • TwiML app Voice request URL: /twilio
  • Twilio phone number Voice URL for a call comes in webhook: /twilio
  • Twilio phone number Voice URL for call status changes: /finished

All these actions are performed for POST request method. You can of course override it by changing the controllers/controller.rb file, but if you just want to install Callio and start using it, you should stick to the addresses above. Of course, all of them should added to your base URL, e.g. So finally our web_client_url in config file should look like

Slack application

When we're done with Twilio, it's time to create a simple Slack application. Go to and create an app (we'll need its token as well). Remember to setup proper permissions of this app to make it able to post the messages on your channel. The only permission we need is chat:write:bot.

Callio setup

Clone the repo, rename config/config.yml.sample file to config/config.yml, fill it with proper data, bundle install and voila! We're done!


To make Callio running on your server you need an environment ready to handle Rack-based application based on Sinatra. In terms of front-end, you have to bare in mind that processing live voice streaming (when you're talking with someone) requires WebRTC/ORTC browser support. Answering the phone calls with the current version of Callio is not possible with every single browser. It works fine with Chrome, Firefox, Opera or Edge, but will not work properly on Safari or mobile device browsers, e.g. Chrome for Android. To check out the current status please use this link.


To communicate with external services we use the following gems:

I want to test it locally...

No problem! You can clone the Callio repo locally and put your app out to the Internets through Remember to update all the webhooks addresses on Twilio and in your config.yml file in order to make it working.


You have to provide some secret data to the config.yml file. A sample config file should look similar to this:

  client_token: 'xoxp-1234-your0slack-99secret4token-nomnomnom3'
  channel: 'awesome-slack-channel-name'
  account_sid: 'ACand0some1random9chars'
  auth_token: '1234rtg42fg234rfgsbh45uknow'
  app_sid: 'APand8your9app3sid9from1twilio'
  client_name: 'your-client-name'
  caller: '+485555555'
web_client_link: ''

What is that? Where do I get all these data?

  • Slack client token - it's a token for authorizing your Slack account when you use the application. First of all, you have to create a Slack application (just give it a name and permissions as above) and you'll get the token when you choose your app under
  • Slack channel - it's just the channel name you want the notifications to be posted, can be actually anything as long as the channel exists
  • Twilio account sid - Get it in your Twilio dashboard after login:
  • Twilio auth token - Just like above:
  • Twilio app sid - You have to create a Twilio app first, go to Console -> Programmable Voice -> Tools -> TwiML apps. After creating a new app you'll get the Application SID there
  • Twilio client name - it's a name you have to type in your Twilio dashboard and Callio config. It authorizes the browser to connect to your Twilio and perform the phone calls
  • Caller - your Twilio phone number
  • Web client link - the endpoint address for your web client - this link is posted on the Slack channel to allow your team members to answer the phone calls in the browser


If you'd like to contribute to Callio, please feel free to do so! I'll be happy to help in case of any questions. For more information please check the contributing guidelines.


This app is available as open source under the terms of the MIT License.