Twilio - Brings voice and messaging to your web and mobile applications.
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.
OpenTok - Build a custom video experience using our robust APIs, or add plug-and-play video to your website in minutes using Video Chat Embeds. Start Building for FreeTalk to SalesTalk to Sales .
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Plivo - Plivo simplifies your customer engagement.
Melrose Labs SMSC Simulator - SMPP SMSC simulator to test SMS messaging applications.