Ryan Kulp built a service called Yelp 3G that allows users to text Yelp to find food faster. The app uses Twilio and sanitizes user input before sending it to the Yelp API. It maintains state by storing historical data in a database, which is used to derive a user's intent with a given message query. The app has features like random search results and drill-down functionality on specific search results. Ryan shares snippets of code that power his app, including a sign-up flow, onboarding process, and message handling logic.