Joe Previte's guide details the creation of a Python application that enables users to identify unknown phone numbers using AWS Lambda, Amazon API Gateway, and Twilio APIs. The app functions by receiving a text message sent to a Twilio phone number, which triggers a POST request via the API Gateway to AWS Lambda. The application then processes the phone number from the message, checks its validity, and uses Twilio's Lookup API to find any associated caller name. Results are sent back to the requester using Twilio's SMS API. The setup involves configuring various AWS services and writing Python scripts for parsing phone numbers, sending messages, and checking caller names. The guide provides step-by-step instructions for setting up the necessary environment, including the creation of a deployment package and linking the Twilio number to the AWS setup. The application aims to alleviate the awkwardness of not recognizing a contact by offering a serverless solution for phone number identification.