Here is a summary of the text in 1 paragraph: This tutorial guides developers through building an API using Symfony, a PHP framework, and integrating it with a mobile application built using React Native. The API uses Vonage's APIs to send notifications via SMS and Text-To-Speech voice calls, enabling a functional on-call system for developers or system administrators to be alerted when issues arise. The tutorial covers setting up the project, building the API, creating a web server, integrating Vonage's APIs, and implementing a mobile application to interact with the API, including displaying alerts and allowing users to accept or cancel them.