The Twilio Add-ons are pre-integrated third-party services that can be used with a Twilio application to enhance the responses received from Twilio by including additional data from Twilio's partners. The IBM Watson Speech to Text Add-on converts Twilio audio recordings into text using machine intelligence and can be integrated with a Sinatra web application using the Twilio Ruby SDK. To use an add-on, it must be enabled in the Twilio Console, where the user selects the recording method, sets the callback URL and request method, and accepts the Terms of Service. The add-on data is then included in the "AddOns" field on HTTP requests made to the application. An example application demonstrates how to access this data within the application, using the IBM Watson Speech to Text Add-on to retrieve the transcription for a recorded call.