Twilio's messaging API provides a simple REST interface for sending SMS and MMS messages, allowing developers to build communications into their apps. The protocol used is SMPP, which is a store and forward protocol that routes messages through multiple servers before reaching the recipient's phone. Despite its limitations, such as character encoding issues, Twilio's API has proven to be highly effective in delivering powerful results for businesses using SMS. With over 100 carriers worldwide, Twilio provides connectivity into all of these carriers, allowing developers to send and receive texts globally. The company's goal is to make customers successful, and its APIs have been instrumental in achieving this by providing a reliable and efficient way to communicate with users around the world.