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Flash Call Verification

Q: What Is A Voice Firewall?

A voice firewall is a security feature used to protect against voice-based attacks on a telephony network. It monitors incoming and outgoing voice traffic, identifies potential security threats, and blocks any unauthorized or suspicious activity. Voice firewalls are commonly used by organizations to secure their telephony systems and prevent fraud or unauthorized access to sensitive information.

Replace manual OTP entry with flash call verification that confirms users through short missed calls and caller ID detection.

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$130B

is the expected valuation for the flash call market by 2026

60%

of costs can be reduced by using flash calls instead of SMS

flash calls were successfully conducted in 2022

What Are Flash Calls?

Flash calls are a phone verification method where a short incoming call is placed to the user’s phone number and automatically disconnected before the call is answered. Instead of receiving a traditional SMS OTP, the last 4-6 digits of the incoming caller ID act as the one-time verification code tied to that authentication session.

In supported mobile applications, the app can automatically read the incoming caller ID in the background, allowing verification to complete without the user manually viewing or entering a code. This creates a faster authentication flow while reducing friction compared to traditional SMS OTP verification.

Immediate and reliable authentication solution

Easily accessible via regular phone calls or other voice channels

Eliminates the need for manual entry or physical devices

If the MNO doesn’t support Flash Call, the verification will automatically fall back to another channel—such as SMS, WhatsApp, or any other option you choose—to ensure your users are verified

How Does Flash Call Verification Work?

Flash call verification starts when a user enters their phone number in an app or website and requests verification. The application sends the request to Dexatel’s Verify API, which immediately places a short automated call to the user’s device. The call disconnects automatically within seconds, usually before the user answers.

The incoming caller ID contains a unique sequence of digits linked to that verification session. On Android devices, the app can automatically detect and read the incoming number in the background for a frictionless experience. On iOS and web environments, users typically enter the last digits of the missed call manually.

Once the digits are captured, the application sends them back to the Dexatel API for validation. The Verify API matches the incoming caller ID against the verification request and confirms whether the authentication attempt is valid. If flash calls are unavailable or unsupported by the carrier, the verification flow can automatically fall back to SMS, WhatsApp OTP, Viber OTP, or other configured channels.

Flash Call API Integration

Initiate the Flash Call

Trigger a flash call by sending an API request with the user’s phone number, verification session details, and any required configuration parameters. The API starts the missed-call verification flow and assigns the caller ID digits.

Detect the Caller ID

Use an Android call detection SDK or app-side logic to read the incoming caller ID automatically where supported. The app captures the last 4-6 digits without requiring the user to type a code manually.

Receive Delivery and Status Updates

Configure webhooks to receive delivery confirmation, call status updates, and verification events in real time. These callbacks help your system track whether the flash call was placed, detected, or failed.

Handle the Verification Result

Send the detected caller ID digits back for validation or process the verification result callback returned by the API. Once the result is confirmed, your application can approve the login, signup, or transaction flow.

Trending Use Cases of Flash Call Verification

App Onboarding

Verify new users quickly during app onboarding using flash call authentication flows. Flash calls help reduce friction during sign-up by allowing automatic phone number verification without manual OTP entry.

Account Recovery

Secure account recovery workflows by verifying that users still have access to their registered phone numbers. Flash call verification can help streamline password reset and account restoration processes.

Device Change and Re-Verification

Re-verify users automatically when they log in from a new device or reinstall an application. Flash call verification helps confirm device ownership while reducing onboarding friction for returning users.

Flash Call vs Other Channels

Factor	Flash Call	SMS OTP	Voice OTP	Email OTP
Cost	Flash calls can be cost-efficient in many regions because verification happens through a short missed call rather than a text message.	SMS OTP pricing is predictable and globally standardized, making it a reliable option for businesses operating across multiple regions.	Voice OTP is typically more expensive because it relies on active voice call delivery and text-to-speech infrastructure.	Email OTP is often the lowest-cost option because it does not rely on telecom infrastructure or carrier delivery.
Speed	Verification is usually completed within seconds, especially when the app can automatically detect the incoming number.	SMS OTP delivery is generally fast, though delivery speed can vary depending on carrier routing and local telecom conditions.	Voice OTP may take slightly longer because users must answer the call and listen to the spoken code.	Email OTP speed depends on inbox delivery, spam filtering, and email provider performance.
Security	Flash calls avoid displaying a visible OTP message and can reduce some phishing or interception risks. They are often used alongside fallback authentication channels.	SMS OTP is widely trusted and commonly used as part of multi-factor authentication strategies across industries.	Voice OTP adds an additional verification layer through direct call delivery and can work well in accessibility-focused environments.	Email OTP benefits from existing email account security layers such as MFA and login monitoring.
UX friction	Flash calls can offer a low-friction experience because users may not need to manually enter a code.	SMS OTP is familiar to most users and requires only basic code entry.	Voice OTP requires users to answer a call and manually enter the spoken code.	Email OTP often involves switching apps or tabs to retrieve the code from an inbox.
Device compatibility	Works best on smartphones and apps that support caller ID detection, though manual verification can also be used.	Compatible with nearly all mobile phones, including feature phones and smartphones.	Works across most mobile and landline devices with voice support.	Works on any device with email access and an internet connection.
Best use cases	Mobile onboarding, cost-sensitive verification flows, and high-volume authentication.	Universal authentication, global verification, and fallback delivery.	Accessibility-focused flows, regions with reliable voice connectivity, and telecom-heavy authentication environments.	Low-cost account verification, desktop workflows, and platforms where users are already email-centric.

Flash Call vs Flash SMS

Flash calls and flash SMS are different technologies used for different purposes. Flash call verification is a voice-based authentication method where a short missed call is placed to a user’s phone number, and the caller ID digits act as the verification code.

Flash SMS is a Class 0 SMS message that appears directly on a device screen without being automatically stored in the SMS inbox. Flash SMS is typically used for urgent notifications or temporary alerts rather than phone number verification workflows.

Flash Call Security and Fraud Prevention

Flash call verification helps reduce friction during authentication while still adding an additional layer of account protection. Each verification request is tied to a unique caller ID pattern or phone number sequence, allowing the platform to confirm that the user has access to the registered device. Since the verification happens through telecom signaling rather than a visible text message, flash calls can also reduce OTP interception and phishing attempts.

At the same time, secure flash call infrastructure still requires strong fraud prevention controls. Rate limiting, request throttling, device fingerprinting, and session expiration help prevent abuse such as repeated verification attempts, bot activity, and artificial traffic generation. Monitoring unusual verification behavior across regions, carriers, and IP ranges can also help identify suspicious activity early.

You can use flash calls as part of a broader multi-channel authentication strategy rather than as a standalone security mechanism. In cases where flash calls are unavailable or unsupported, platforms can automatically fall back to SMS OTP, WhatsApp OTP, or voice verification to maintain both security and delivery reliability.

What Is a Voice Firewall?

A voice firewall is a telecom security system designed to detect, filter, and block fraudulent or suspicious voice traffic before it reaches users or business infrastructure. It helps mobile operators and communication platforms prevent threats such as robocalls, artificial traffic generation, spoofed caller IDs, Wangiri fraud, and unauthorized international routing.

Voice firewalls analyze signaling patterns, call behavior, traffic anomalies, and routing activity in real time to identify suspicious activity. In authentication environments like flash call verification, voice firewall protections can also help reduce abuse attempts, fake verification traffic, and carrier manipulation that may increase costs or disrupt legitimate verification flows.

Price per Flash Call Verification

Country	Price
United States	From $0.01836
Brazil	From $0.00561
Italy	From $0.01166
Germany	From $0.011
Japan	From $0.0121

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Flash Calls Pricing Model

Flash call verification pricing uses a pay-per-verification model, with flash call verification cost determined by destination country, carrier routing, traffic volume, and fallback configuration. Per flash call pricing and flash calling rates may also vary depending on route quality, regional telecom requirements, and authentication volume tiers.

Compared to SMS OTP, flash calls can reduce per-verification costs in many regions, especially for high-volume mobile authentication workflows. Businesses sending large authentication volumes can often access lower flash calling rates through volume-based pricing agreements.

Trending Use Cases of Flash Call Verification

2F Authentication

Transaction Authorization

Identity Verification

Password Reset

App Onboarding

Account Recovery

Device Change and Re-Verification

2F Authentication

Take your security up a notch by using flash calling authentication as a second factor. Users enter their password via a flash call instead of SMS authentication to ensure security.

Transaction Authorization

Confirm purchases, fund transfers, and other sensitive actions using flash call verification. Users receive a short missed call linked to the authorization request before the transaction is approved.

Identity Verification

Opt for a secure and efficient identity verification solution with flash calls or Verified SMS, especially in the healthcare and finance sectors so users can securely access sensitive info.

Password Reset

Authenticate users during password reset flows using flash call authentication. Flash calls can help simplify account recovery while reducing manual code entry during the reset process.

App Onboarding

Account Recovery

Device Change and Re-Verification

Integrate Flash Call Verification in Minutes

Integrate flash call verification into your application using APIs, automatic caller ID detection, webhook callbacks, and mobile authentication workflows designed for scalable user verification.

Let’s Get in Touch

Build faster mobile authentication flows with flash call verification, automatic caller ID detection, and API-driven user verification. Talk to our team about integrating flash calls into your onboarding, login, and authentication systems.

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Got Questions? We’ve Got Answers

What is an A2P flash call?

An A2P flash call is a type of automated phone call service that is initiated by a business or organization as part of their application-to-person messaging strategy. A2P flash calls are often used in industries such as finance, healthcare, and eCommerce, where security is of the utmost importance.

How does flash call verification work?

When a user attempts to log in to an application or website that uses flash calls, they will receive an automated phone call with a verification code. The user then enters the code into the application or website to verify their identity.

Are flash calls good for the user experience?

Yes, flash calls can be good for user experience as they provide a quick and user-friendly authentication method. Since they only require a user to answer an automated call and enter a verification code, it can be a more seamless authentication process compared to traditional password-based authentication methods.

What devices are compatible with flash calls?

Flash calls are compatible with all mobile devices with an iOS or Android operating system. With Android, the code is processed automatically. However, with iOS or the web, users must input the code manually.

Are flash calls cost-effective?

Yes, flash calls are quite affordable. According to studies, using flash calls can result in about 60% cost reduction compared to using SMS for authentication purposes. This is due to the fact that flash calls use VoIP technology, which allows for the transmission of voice and data over the internet, eliminating the need for traditional telephone networks and associated charges.

What happens when I get a missed flash call?

If you receive a missed voice call, it means that the authentication process was not completed successfully. To verify your identity, you will need to initiate the process again and receive a new flash call with a unique code to enter.

Are flash calls more secure than SMS?

Flash calls and SMS OTP each offer different security advantages. Flash calls reduce reliance on visible text messages and can lower some phishing or interception risks, while SMS OTP remains one of the most trusted and widely adopted authentication methods globally. Many businesses combine multiple channels together for stronger authentication resilience and delivery reliability.

What is the difference between flash calls and OTP?

OTP (one-time password) is the authentication code itself, while flash call is one delivery method used to verify a user’s identity. Instead of sending a visible code through SMS or email, flash call verification uses an incoming phone number or caller ID pattern tied to the verification session. The user or application then confirms the digits to complete authentication.

Do flash calls work on iPhone?

Yes, flash calls can work on iPhone devices, though the experience differs from Android. Due to iOS platform restrictions, apps typically cannot automatically detect incoming caller ID digits in the background the same way Android apps can. In most iPhone verification flows, users manually enter the last digits of the incoming call to complete verification.