Twilio - Brings voice and messaging to your web and mobile applications.
Digsby - Tagged makes it easy to meet and socialize with new people through games, shared interests, friend suggestions, browsing profiles, and much more.
Plivo - Plivo simplifies your customer engagement.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.