To send an SMS with Java and the Spark framework, you need to set up a Twilio account and install ngrok. Then, create a new Java project in IntelliJ IDEA, add the necessary dependencies, and write a Java class that responds to incoming SMS messages with a text message. After running the application, set up a webhook with Twilio using ngrok's public URL and configure it to send incoming message notifications to your Java application. Finally, test the application by sending a text message to your Twilio phone number on your mobile device.