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What is Flash Call verification?

Last reviewed 1 min readReviewed by BroadNet engineering
Quick answer

Flash Call is a number-verification technique that places a missed call to the user's phone with a one-time short MSISDN as the caller-ID. The user's app reads the last 4-6 digits of the incoming caller-ID — that is the OTP — and the call is hung up before it rings. The user sees nothing; the verification completes silently. It is faster, cheaper, and harder to spoof than SMS OTP.

Plain-language definitionVendor-neutralReviewed May 27, 2026
DiagramThe OTP journey, with channel fallback
  1. User requests a codeSign-in, payment or sign-up
  2. Your app calls the verify APIOne request per code
  3. BroadNet delivers the codeOn the best available channelFallback if undeliveredSMSWhatsAppVoice
  4. User enters the codeChecked against the issued code
  5. VerifiedAccess granted
The long answer

Everything worth knowing, nothing that isn't.

§01

How it works end-to-end

Your app calls our /verify/start with a phone number and method=flashcall. We dial the number from a single-use MSISDN whose last digits encode the OTP. The Android CALL_LOG permission lets your app read the incoming caller-ID; it strips the last 4-6 digits, hashes them, and POSTs to /verify/check. If the hash matches, the user is verified. End-to-end: 3-5 seconds. Cost: 30-60% of SMS OTP.

§02

Why operators love it

Flash Call doesn't touch the SMSC, doesn't consume a billable SMS event, and doesn't burn an A2P trunk. It is a single CAMEL/SIP call setup that gets cancelled before connect — most operators treat it as an unanswered call (free or near-free). For high-volume OTP services in markets where SMS A2P pricing is punishing (India, Indonesia, Brazil), Flash Call drops verification cost dramatically.

§03

Where it doesn't work

iOS apps cannot read incoming caller-ID programmatically. Flash Call is Android-only (and only via the user granting CALL_LOG, which Google has been increasingly restrictive about — Android 11+ requires the app to be the default Caller ID app or use SMS_RETRIEVER as a fallback). Always pair Flash Call with an SMS-OTP fallback. BroadNet's /products/myotp service auto-falls-back from Flash Call → SMS OTP → WhatsApp OTP → Voice OTP in a single API call.

§04

Regulatory state

GSMA published RCC.20 guidelines for Flash Call in 2022, treating it as a legitimate verification technique. Some operators (parts of India, the UAE) have started classifying it as A2P and applying A2P pricing; others (most of MENA, EU) still treat it as a voice event. Pricing varies accordingly. We track per-country classification and price accordingly.

BNWritten by the BroadNet engineering team·Operating carrier-grade messaging since 2003, headquartered in Dubai·Editorial standards
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