Twilio - Brings voice and messaging to your web and mobile applications.
andOTP - andOTP is a two-factor authentication App for Android 4.4+
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Authy - Best rated Two-Factor Authentication smartphone app for consumers, simplest 2fa Rest API for developers and a strong authentication platform for the enterprise.
Sinch - Sinch is a powerful voice and messaging SDK that lets you bring your apps to life with VoIP and...
Google Authenticator - Google Authenticator is a multifactor app for mobile devices.