This tutorial provides a comprehensive guide on how to add voice interaction to an existing text-only chatbot using Vonage Voice API for speech recognition and text-to-speech capabilities. The application uses the Node.js server SDK '@vonage/server-sdk' and supports over forty language locales for both Automatic Speech Recognition (ASR) and Text-to-Speech (TTS). The tutorial covers a two-phase approach, starting with a local deployment on a computer to illustrate how to voice-enable a text chatbot, followed by an optional deployment to Heroku-hosted environments. The second phase involves updating the source code of the Voice API application to integrate with the actual chatbot for text requests/responses. Throughout the tutorial, developers can learn how to use Vonage Voice API to enable their chatbots to listen to callers' spoken requests and playback replies, making it a valuable resource for those looking to enhance their chatbot's functionality.