In this guide, we'll cover how to combine Twilio Add-ons with Programmable Voice to use data from Twilio's partners in your Express web application. Twilio Add-ons are pre-integrated third party services that enhance the responses your application receives from Twilio by including additional data from Twilio's partners. The sample code uses the Twilio Node SDK and the Express web framework, starting with the IBM Watson Speech to Text Add-on. To use an add-on, first enable it in the Twilio Console, then select the recording method and set a callback URL. In your application, access add-on data within an "AddOns" field on HTTP requests. The guide demonstrates how to use the IBM Watson Speech to Text Add-on to convert Twilio audio recordings into text using machine intelligence.