The author, Robert Welbourn, explains how to build sophisticated Twilio Programmable Voice apps using a JavaScript toolkit that incorporates Node.js and the Express web application framework. The toolkit uses Promises to handle webhooks and status callbacks, which are delegated to an Express-based web application running under Node.js. The developer is free to create their application in a natural, top-down way without the complexity of writing a state machine. The author provides examples of how to use the toolkit, including building a conference call app that handles inbound calls and makes outbound calls to other participants in parallel. He also discusses topics such as scaling, redundancy, and logging, which are important considerations for building scalable and resilient applications using the Programmable Voice Toolkit.