This tutorial demonstrates how to send an SMS message during a phone call using Twilio's Programmable Voice and SMS APIs with Java and Spark web framework. The application accepts incoming calls, says something to the caller, and sends them a text message using Twilio's SMS API. The code handles exceptions for cases where the recipient is unable to receive SMS messages, such as when calling from a landline in certain locations. The app uses environment variables to store sensitive information like account SID and authentication token, ensuring secure access to these credentials.