What is the difference between SMS OTP, Voice OTP, Flash Call and Silent Network Authentication?

An OTP Authenticator provider typically offers multiple verification methods through a single platform. SMS OTP authentication sends a 6-digit code to the user's phone for manual entry. Voice OTP places an automated call and reads the code aloud, making it ideal for feature phones. Secure voice OTP authentication services add another layer of reliability for businesses that need dependable voice-based verification. Flash Call uses the last four digits of a missed call as the OTP, while Silent Network Authentication (SNA) verifies the user's SIM through a carrier API without any user interaction. SMS works across all devices, Voice supports feature phones, Flash Call requires Android with call log permission, and SNA currently supports Airtel and Jio in India.