Handle Keypad Input (DTMF) with PHP

The code provided is for a PHP application that can receive inbound calls and capture user input entered via the keypad, utilizing the Vonage API and the Slim framework. To set up this application, one needs to have a Vonage API account, a virtual phone number, and PHP 5.6 or above installed. The application will respond to incoming calls by displaying text prompts and capturing DTMF input from the caller, which is then sent to a separate URL for processing. The code uses ngrok to expose the local server to the internet, allowing Nexmo to make requests to it. Once set up, the application can be tested by dialing the associated phone number and following the steps spoken on the other end of the line.