What are some alternatives?
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
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.
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.
Twilio - Brings voice and messaging to your web and mobile applications.
Wire - Private & Secure Messenger
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates