Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Twilio - Brings voice and messaging to your web and mobile applications.
VerifyKit - Enables quick access to your web and mobile applications.
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Sinch - Sinch is a powerful voice and messaging SDK that lets you bring your apps to life with VoIP and...
Authy - Best rated Two-Factor Authentication smartphone app for consumers, simplest 2fa Rest API for developers and a strong authentication platform for the enterprise.