This post demonstrates how to use Twilio Lookup in a .NET Core WPF application, providing a way to validate phone numbers and determine if they are capable of receiving SMS text messages. The process involves adding the Twilio NuGet package to the project, creating a data model for Twilio credentials, designing the user interface, coding the event handlers, and handling API errors. The code uses environment variables to securely store Twilio account credentials and utilizes the `TwilioClient` object to establish a secure connection with the Twilio REST APIs. The application allows users to enter phone numbers and verify them using Twilio Lookup, displaying the results in E.164 format if successful. The post provides additional resources for learning more about Twilio and .NET Core development.