Authentication

Voice OTP routes for verification that works first time

Direct voice OTP for fintech, wallets and identity platforms, including the markets where SMS OTP is filtered or delayed. Clear audio, and a fallback path when the first attempt fails.

Routes chosen for answer rate, not just cost
Works where SMS OTP is filtered or delayed
Resistant to SIM-swap and message interception

Request a Voice OTP test route See the specification BD · IN · PK live

At a glance HTTPS REST API or SIP interconnect CLI and non-CLI paths depending on destination Text-to-speech or pre-recorded prompt, repeat on request Multiple locales, including regional South Asian voices

Specification

The numbers, up front

Destination-level coverage

Connection: HTTPS REST API or SIP interconnect
Routing: CLI and non-CLI paths depending on destination
Audio: Text-to-speech or pre-recorded prompt, repeat on request
Languages: Multiple locales, including regional South Asian voices
Retry logic: Configurable re-attempts and SMS fallback ordering
Reporting: Per-call disposition, answer state and duration in CDRs
Best for: High-value verification and SMS OTP recovery
Typical volume: Agreed per account, with burst capacity on request

What you get

Why platforms add a voice channel to verification

Voice OTP is not a replacement for SMS OTP. It is the channel that recovers the users SMS loses, and in some markets that is a double-digit share of your signups.

Harder to intercept than SMS

A spoken code is not sitting in a message store, is not forwarded by a compromised handset, and does not arrive on a SIM someone else has just swapped. For high-value actions that difference matters.

Reaches users SMS cannot

Where A2P messaging is filtered, throttled or blocked, a voice call still completes. In several South Asian and African markets this is the difference between a user signing up and giving up.

Routed for answer rate

Paths are selected on whether calls are answered and completed, not only on termination price. A cheap route with a low answer rate costs more per verified user.

Designed as a fallback, not a silo

Trigger voice automatically when an SMS OTP is not confirmed within your chosen window, on the same account and the same balance.

Accessible to users who cannot read the message

Feature phones, low-literacy users and visually impaired users are all served better by a spoken code than a text one.

Per-call visibility

Answer state, duration and disposition per attempt, so you can see whether a failure was the route, the number or the user.

Where SMS OTP quietly fails

Most verification funnels are measured on messages submitted, not on users verified. That gap is where voice OTP lives. A message can be accepted by the network and still never reach the user, filtered by an operator firewall, delayed past the point of usefulness, or delivered to a handset that has just been swapped onto a different SIM.

The failure modes worth planning for:

Filtering. Operator anti-spam systems block traffic that pattern-matches to bulk, and OTP messages look very like bulk.
Latency. A code that arrives after ninety seconds has usually arrived after the user has abandoned the form.
SIM swap. The message is delivered correctly, to the attacker.
Handset reality. Feature phones, full inboxes, and users who cannot read the message at all.

Voice as a recovery channel, not a replacement

The pattern that works is simple: send the SMS first because it is cheaper and less intrusive, and place a voice call when the SMS is not confirmed inside your window. Doing that reliably needs both channels on one account, so the retry logic is a single decision rather than a second integration.

What we optimise for

Voice OTP routing is judged on whether calls are answered and completed. Termination price is a constraint, not the objective, a cheaper route with a materially lower answer rate costs more per verified user, and we will say so.

Use cases

Where voice verification earns its place

Fintech and mobile wallet onboarding

Verification for account creation, device binding and high-value transfers, where a failed OTP is a lost customer.

Account recovery and password reset

The step where SMS delivery failure is most expensive, because the user has no other way back in.

High-value transaction confirmation

Second-channel confirmation for transfers, withdrawals and beneficiary changes.

Markets with unreliable A2P messaging

Destinations where SMS OTP delivery is inconsistent enough that a voice fallback pays for itself.

Feature-phone and low-literacy user bases

Spoken codes reach users a text message cannot serve.

SIM-swap risk reduction

Part of a layered defence for accounts where the cost of takeover is high.

How it works

How a voice OTP call is placed

Your platform requests a code

One API call, or a SIP invite, carrying the destination number and the code to be spoken.
We select the route

Destination, time of day and current answer rate decide the path, CLI or non-CLI as the market requires.
The call is placed and the code read

Clear text-to-speech or your own recording, repeated automatically if the user asks.
Disposition returns to you

Answered, unanswered, busy or failed, with duration, so your retry and fallback logic has something real to act on.

Connect

How to connect Voice OTP

Every method reaches the same routes, the same balance and the same reporting. Pick the one that suits how your platform is built.

Compare all connection methods

SMPP v3.4 bind

SMPP v3.4

An SMPP v3.4 bind is the standard way to move A2P SMS at volume. Transmitter, receiver or transceiver, with real…

Set up SMPP v3.4 bind

HTTP REST API

HTTPS / JSON

A straightforward HTTP REST API in JSON, for teams that would rather not run a persistent SMPP session. Same routes,…

Set up HTTP REST API

SIP interconnect

SIP / RTP

A SIP interconnect for voice termination, Voice OTP and TTS, with an engineer on the call for interop.

Set up SIP interconnect

IP authentication

IP allow-list

IP authentication instead of credentials: authenticate by source address, for platforms with fixed egress IPs.

Set up IP authentication

Coverage

Destination availability

Search for the destinations you care about. Anything not listed is usually available on request, capacity is added weekly.

Route availability by destination
Destination	Dial / MCC	A2P SMS	Voice OTP	TTS voice	Termination
Bangladesh	+880 · 470	Live	Live	Live	Live
India	+91 · 404 / 405	Live	Live	On request	On request
Pakistan	+92 · 410	Live	Live	On request	Live
Nepal	+977 · 429	On request	Live	On request	On request
Sri Lanka	+94 · 413	On request	Live	On request	On request
Indonesia	+62 · 510	Live	On request	On request	On request
Philippines	+63 · 515	Live	On request	On request	On request
Vietnam	+84 · 452	On request	On request	No	On request
Malaysia	+60 · 502	Live	On request	On request	On request
United Arab Emirates	+971 · 424	Live	On request	No	On request
Saudi Arabia	+966 · 420	Live	On request	No	On request
Oman	+968 · 422	On request	On request	No	On request
Qatar	+974 · 427	On request	On request	No	On request
Egypt	+20 · 602	On request	On request	On request	On request
Nigeria	+234 · 621	Live	On request	Live	On request
Kenya	+254 · 639	On request	On request	On request	On request
South Africa	+27 · 655	On request	On request	No	On request
Turkey	+90 · 286	On request	On request	No	On request
United Kingdom	+44 · 234	Live	On request	No	On request
United States	+1 · 310	On request	On request	No	On request

See 14 more destinations Show fewer

Why SisBird

What makes a voice OTP route good

Answer rate is the metric that matters

A verification call that is not answered has not verified anyone. We optimise routing on completion, and we will tell you when a destination is performing badly rather than letting you discover it in your funnel.

Voice and SMS on one balance

Run SMS OTP as primary and voice as fallback without a second supplier, a second contract or a second reconciliation process.

Capacity for the spike

Verification traffic is bursty, a campaign, a launch or an outage elsewhere. Capacity is provisioned for the peak, not the average.

Who runs these interconnects

Next step

Test Voice OTP against your real failure cases

Send us the destinations where your SMS OTP is failing. We will route them by voice on a test account and you can compare completion rates directly.

1
You send the brief Destinations, monthly volume and the traffic type. Two lines is enough.
2
A routing engineer replies A costed plan with the route type stated per destination, usually within one business day.
3
You test on funded credit Same interconnects production runs on. No minimum term and no setup fee.

Or reach the routing team directly

Request a test route

For Voice OTP. We reply within one business day.

Reply within one business day Free test credits on approval No spam, no reselling of your data

FAQ

Voice OTP questions

What is a Voice OTP route?

A voice OTP route is the path used to place an automated call that reads a one-time password aloud to the user. It is used either as the primary verification channel or as a fallback when an SMS OTP is not confirmed.

Is Voice OTP more secure than SMS OTP?

For some threat models, yes. A spoken code is not stored in a message inbox, is not forwarded automatically by a compromised device, and is less exposed to SIM-swap and SMS-interception attacks. It is not immune, a determined attacker with call-forwarding control can still intercept, so it is best used as one layer among several.

When should I use voice instead of SMS?

Use SMS as the default for cost, and voice for high-value actions, account recovery, and any destination where your SMS completion rate is poor. Most platforms end up running both, with voice triggered automatically after an SMS attempt goes unconfirmed.

Do you support CLI on voice OTP calls?

Where the destination market permits it. Some markets require a registered CLI, some prohibit alphanumeric or foreign CLI on automated calls, and some allow non-CLI delivery only. Our coverage records the rule per destination.

What languages can the code be read in?

Multiple locales including regional South Asian voices, or you can supply your own recorded prompt and we insert the digits into it.

How does the fallback from SMS work?

You choose the window. If your platform has not confirmed the SMS OTP within it, you call the voice endpoint with the same code. Both channels sit on one account, so there is nothing extra to reconcile.

Read every wholesale routing question we are asked

Also available