This tutorial guides users through building a Vonage Voice API-powered contact center solution using ASP.NET Core, allowing customers to leave voicemails when no one answers the phone. The solution involves creating an application in the Vonage Dashboard, linking a virtual phone number to it, and setting up an Answer webhook that uses the Nexmo Call Control Object (NCCO) to record calls. The code is written in C# using ASP.NET Core and utilizes dependency injection for configuration management. Once set up, users can call their assigned Vonage API number, leaving a voicemail that gets recorded and saved to a local file.