Twilio and OpenAI are used to create an audio-to-text translator that receives audio messages via WhatsApp, transcribes them with OpenAI's Whisper API, and responds with the transcription as a TwiML message. The application uses .NET Core to build a WebAPI project that interacts with Twilio's WhatsApp messaging service and OpenAI's Speech to Text API to process the received audio files. It also utilizes FFmpeg to convert unsupported audio formats to wav-format before sending them to OpenAI for transcription. The code includes error handling, authentication, and validation mechanisms to ensure the application is secure and reliable.