To prevent robocallers from leaving voicemails, Twilio users can install and configure the Trestle Reverse Phone Add-on, which provides caller information. This add-on must be used with Twilio Functions, a serverless Node.js platform for deploying code. The user creates a Twilio Function to handle incoming calls, parses the data from Trestle Reverse Phone, and dynamically generates TwiML instructions based on that data. If the caller's phone number is valid, they are prompted to leave a voicemail; if not, the call is rejected with <Reject>. After purchasing and configuring a Twilio Phone Number with Voice capabilities, the user can try out the setup by calling their own phone number. The Twilio Console provides access to view the data from Trestle Reverse Phone in Call Logs, as well as listen to recordings.