Or, simply, Horntones. "The Horntones FX-550 system is the first mobile audio system that allows you to customize the sound of your vehicle’s horn function using virtually any standard audio file."
How would you get the tunes to your car? Elementary. Through a fuel dispenser that "is an Internet-ready, WiFi-capable gas pump with a 15-inch touchscreen and speakers, which enables the transfer of media content to other WiFi-enabled devices." Dresser Wayne Ovation²® iX.