What are some alternatives?
Twilio - Brings voice and messaging to your web and mobile applications.
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.
Melrose Labs SMSC Simulator - SMSC simulator to test your SMS applications and messaging infrastructure.
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.
HSL SMS Gateway - SMS messaging service suitable for enterprise, school and business SMS uses. Reliable and fast SMS delivery using SMS APIs and solutions. SMS Gateway providing SMPP, HTTP, Web Service and SMTP APIs plus AlertBroadcast, EmailSMS and WebSMS.