Callr is a service that eliminates the need for entering conference PINs, making it easier to join meetings without frustration. The company's CEO, Mike Endale, and his team were frustrated with the proprietary systems used by various platforms, leading them to build a universal key that connects all conference platforms. By leveraging Twilio's API, Callr's service was built quickly and efficiently, allowing users to focus on what matters most - attending meetings without hassle.