Clockwork is an easy text message API. An SMS API just for developers. Build powerful apps and include SMS. Signup is free, try it now.
Nexmo is a simple API to push SMS at wholesale rates with high deliverability. Reach over 4 billion mobiles in more than 200 countries.
Twilio lets you use standard web languages to build voice, VoIP and SMS applications via the web. Build the next generation of communications with us.
46elks is a cloud communications platform which makes it very easy to integrate Voice and SMS into your applications.