What are some alternatives?
Twilio - Brings voice and messaging to your web and mobile applications.
Plivo - Plivo's Voice API enables businesses to build Voice apps to reach customers globally in 200+ countries. Try Plivo's Voice API for free. Instant Sign Up.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Clockwork SMS - Clockwork is an Easy Text Message API. An SMS API for Developers. Build powerful apps and include SMS. Signup is free, Try it now.
MessageBird Cloud communications platform - MessageBird is an enterprise-grade cloud communications platform offering API solutions for SMS, Voice and Chat for +15,000 businesses.
Bandwidth - Track your Wi-Fi hotspot usage. Zero configuration required. It just works.