It's easy to be skeptical about startups who promise to change the world, but when Twilio says that it's "reinventing telecom by merging the worlds of cloud computing, web services and telecommunications" it's actually a highly accurate description. The API allows third party companies to simply implement telecommunications features without the need to build their own. Say for example you've just started an Uber like company and you want to have SMS messages sent as booking confirmations, this is where Twilio would step in with its API. With access to the API you add the code to your shiny new Uber like startup and bingo, you now have SMS support without having to spend a pile of money building the app feature from scratch.