For easing app developer's headaches by letting them add voice, SMS and VoIP functionality to their apps. Twilio provides easy-to-integrate phone and text services to its 75,000 developers. "The number-one thing we did was create access to telecommunications for developers, when before it was this black box," says Danielle Morill, Twilio's director of developer evangelism and the startup's first hire. In 2011, it quadrupled in size to more than 100 employees and increased its customer base by 400%. Last year it launched Twilio Connect, easing the billing process between developers and their users, and Twilio Client, allowing developers to integrate cloud communications into their apps. They also expanded into Europe.