The add-on lets you connect the Twilio.com SMS provider to send SMS messages for user phone verification, which can be used during registration.
In addition, the plugin can deliver notifications via WhatsApp through the same Twilio account – a separate channel that you enable in the plugin settings and turn on per notification template. A WhatsApp text is optional: when left empty, the notification's SMS text is sent instead, so the channel works out of the box. Notifications are delivered to the user's own phone number from their profile.