A .NET developer can create a web application that uses Twilio to phone friends using Blazor and C#. The application is built with Visual Studio 2019, includes an API project for handling Twilio calls, and uses Ngrok to tunnel the API to the public internet. A Blazor page is created to handle user input, such as entering a phone number, and wire up buttons to initiate and end phone calls. The application also logs messages to display in the UI. To use the application, start a Ngrok tunnel in Visual Studio, configure Twilio's client SDK, and run the application.