Twilio is a cloud communications IaaS (Infrastructure as a Service) company based in San Francisco, California. Twilio allows software developers to programmatically make and receive phone calls and send and receive text messages using its web service APIs. Twilio's services are accessed over HTTP and are billed based on usage. As of October 2012, more than 150,000 developers use the service. Twilio is reinventing telecom by merging the worlds of cloud computing, web services and telecommunications. Twilio hosts a telephony infrastructure web service in the cloud, allowing web programmers to integrate phone calls and SMS messages into their applications. Twilio's simple, powerful API minimizes the learning curve required to build advanced, reliable communications applications, and its Pay-As-You-Go pricing model means customers pay for capacity only when they need it, not before.