How I replaced Skype with Twilio (2019–2022)

How I replaced Skype with Twilio to make phone calls from my computer.

Motivation

Working remotely, I have become used to the comfort of making calls from my computer on Slack or Discord. Using a quality headset gives a warm sound and a feeling of proximity, and leaves the hands clear for typing on the keyboard and looking up information during the call.

I have been a longtime subscriber of Skype premium service to get a similar experience when calling regular phones instead of other computers. Sadly, as the Skype service stagnated for many years before changing for the worse in 2017–2018, I had to find a better alternative and I started to look into VOIP services with support for calls to the PSTN in 2018–2019.

The Long Story

This is the story of how I successfully configured Twilio to get a mobile phone number which can make and receive calls from my computer.

I have described all the steps that I followed in details, including the understanding that I gained through trial and error, in separate issues:

• How Skype dumped me
• How I compared different VOIP providers
• How I chose a mobile phone number on Twilio
• How I tried two different VOIP software phones
• How I configured Twilio to send/receive phone calls
• How I configured Twilio to record voicemail and send it to me by email
• How I compared different services to send/receive SMS messages by email
• How I configured Twilio and Pipedream to send/receive SMS messages by email
• How I managed to receive authentication SMS messages

If you are interested only in how to reproduce my current setup, you can read the short story below. It features links to more details in the long story, if you need them.

The Short Story

1. Create your Twilio account

• if you do not have a Twilio account, sign up
• or if you already have a Twilio account, sign in

2. Choose a new phone number

• register a credit card
• add funds to your account
• purchase a new phone number

3. Configure SIP

• create a SIP user for yourself
• create a SIP domain for your Twilio phone number
• download and install Linphone on your computer
• configure call encryption and add the SIP user in Linphone

4. Make calls from your computer

• create a TwiML script which describes how phone calls made from the computer are forwarded to regular phones:

<?xml version="1.0" encoding="UTF-8"?>
<!-- Making Calls from SIP to Regular Phones -->
<Response>
  <Dial callerId="{{#e164}}{{SipDomain}}{{/e164}}">
    {{#e164}}{{To}}{{/e164}}
  </Dial>
</Response>

• copy the URL of the TwiML bin, found in its details after saving the script.

• go to the settings of the SIP domain, and under Voice Configuration, paste the URL from the clipboard into the Request URL field

• save the settings of the SIP domain

• launch Linphone on your computer

• test the setup: call a regular phone number from Linphone

• you can then save this phone number as a contact

5. Receive calls on your computer

• create a new TwiML script which describes how phone calls received from regular phones are answered:

<?xml version="1.0" encoding="UTF-8"?>
<Response>
  <!-- Receiving Calls from Regular Phones to SIP -->
  <Dial>
    <Sip>sip:[email protected];transport=tls;secure=true</Sip>
  </Dial>
</Response>

In the above script, replace the user name and domain in the <Sip> element with the identifier of the SIP user that you created, followed with @ and the SIP domain that you created, ending with .sip.us1.twilio.com;transport=tls;secure=true:

<Sip>sip:[SIP User]@[SIP Domain].sip.us1.twilio.com;transport=tls;secure=true</Sip>

• go to the configuration of your phone number on Twilio

• next to "A call comes in", select TwiML and the script that you just created to manage incoming phone calls

• delete the URL next to "A message comes in", which answers all texts with a canned response

• save the settings

• try to call your Twilio number from a regular phone

6. Configure a voicemail

You can extend the TwiML script which handles incoming calls to forward the caller to voicemail when you fail to answer:

• record a voicemail greeting using Audacity
• export the greeting as a WAV file (in mono with 8bit/s at 8kHz)
• upload the WAV as an asset on Twilio
• copy the URL of the asset
• go to the Voicemail Twimlet
• [create a custom Voicemail URL][] using the generator form at the bottom of the page:
  • Email: the email address where you want to receive voicemail notifications
  • Message: the URL of your greeting, pasted from the clipboard
  • Transcribe: false
• copy the generated URL
• go to the Forward Twimlet
• create a custom Forward Twimlet URL: paste your custom Voicemail URL next to FailUrl in the form at the bottom of the page, then change its protocol from http to https
• leave all the other fields empty
• copy the generated URL
• go back to your Twilio dashboard
• in the TwiML bin which handles incoming calls, add an action attribute to the <Dial> element
• paste your custom Forward URL as its value
• change the protocol of the URL from http to https
• then add &Dial=true at the end of the URL

You now have a script of the form:

<?xml version="1.0" encoding="UTF-8"?>
<Response>
  <!-- Receiving Calls from Regular Phones to SIP (with Voicemail) -->
  <Dial action="https://twimlets.com/forward?FailUrl=https%3A%2F%2Ftwimlets.com%2Fvoicemail%3FEmail%3Dyou%2540example.org%26Message%3Dhttps%253A%252F%252Fyour-runtime-domain.twil.io%252Fassets%252Fgreeting.wav%26Transcribe%3Dfalse&amp;Dial=true">
    <Sip>sip:[email protected];transport=tls;secure=true</Sip>
  </Dial>
</Response>

where:

• [email protected] stands for your email address
• https://your-runtime-domain.twil.io/assets/greeting.wav stands for the URL of your greeting asset
• your-sip-user stands for the SIP user that you created for yourself
• your-sip-domain stands for the custom SIP subdomain that you created

• you can now close your computer and call your Twilio number from a regular phone to test the voicemail

7. Configure Pipedream Workflow to Send SMS Messages by Email

• create your Pipedream account]
• a new workflow is created automatically, rename it to Send SMS by Email
• select the Email action for the trigger step of the workflow
• send a test email to the inbound email address of the workflow

When sending an SMS by email, you will need to include the phone number of the recipient, in international format, in the subject, e.g. New SMS to +## ###-###-#####.

• the test event is received by your Pipedream workflow
• continue and add the Twilio: Send SMS action as a second step
• create a Twilio API key and connect Pipedream to Twilio API
• select your Twilio phone number as From
• configure the following template as To:

{{steps.trigger.event.headers.subject.replace(/^.+\+/,'+').replace(/[^+0-9]/g,'')}}

• configure the following template as Message Body:

{{steps.trigger.event.body.text}}

• test and deploy the configured workflow

8. Configure Pipedream Workflow to Receive SMS Messages by Email

• create a new workflow
• name it Receive SMS by Email
• select HTTP / Webhook Requests as trigger step of the workflow
• configure a static response for the webhook, with status code 200, header Content-Type:application/xml and the static response below:

<?xml version="1.0" encoding="UTF-8" ?>
<Response/>

• configure the trigger URL as webhook for incoming SMS in Twilio dashboard
• send a test SMS to your Twilio phone number
• the test event is received by your Pipedream workflow
• continue and add the Send Email action as second step of the workflow
• configure the template below as Subject:

New SMS from {{steps.trigger.event.body.From}}

• configure the template below as Text:

{{steps.trigger.event.body.Body}}

• test and deploy your second workflow

Limitations

The current setup does not fulfill all of my expectations yet:

• even for calls from Europe to Europe, the call always transits through a Twilio server in the US, increasing latency

License

• Code: CC0 (no attribution required)
• Text and Images: CC-BY Eric Bréchemier