Transactional Voice SMS & Voice OTP — Automated Voice Calls for OTP, Alerts & Reminders
Deliver one-time passwords, alerts and reminders as automated voice calls — text-to-speech in Hindi and regional languages or pre-recorded audio, DTMF capture and instant voice-OTP failover when an SMS doesn’t land. Direct operator connects across India, with reach in 190+ countries.
What is transactional voice SMS (OBD)?
Transactional voice SMS — also called an outbound dialer (OBD) or voice broadcast — is an automated phone call that plays a pre-recorded clip or a text-to-speech message to deliver an OTP, alert, reminder or confirmation. Instead of reading a text, the recipient simply answers and hears the message spoken aloud.
Unlike a text SMS that can sit unread or fail on a congested network, a voice call rings the handset and speaks the content directly — ideal for time-critical OTPs, EMI reminders and service alerts, and reachable even on basic feature phones. It works alongside your transactional SMS, adding an audible channel that lands when text alone isn’t enough.
Voice OTP — the reliable OTP fallback
A voice OTP is a one-time password read aloud over an automated call. An IVR speaks the code digit-by-digit (and can repeat it on request), so users complete verification even when SMS is delayed, blocked or undelivered.
How it works
Your app triggers the call; the IVR dials the user and reads the code aloud, clearly and slowly, with an option to hear it again.
Voice OTP vs SMS OTP
Voice connects in seconds, boosts success on weak networks and resists SIM-swap SMS interception — a strong complement to text OTP.
Automatic failover
Trigger a voice OTP automatically when an SMS OTP isn’t delivered within a set window — near-100% reach without manual retries.
How the outbound dialer works
Trigger
Fire a call via REST API or upload a contact list on the web panel with your message.
Gateway
Our voice gateway queues the call and renders TTS or loads your pre-recorded audio.
Operator connect
Direct connects with Jio, Airtel, Vi and BSNL route the call to the recipient.
Call answered
On pickup, the IVR plays the OTP or message aloud and can repeat it on request.
Status returned
DTMF keypresses and call status (answered, voicemail, failed) post back to your app.
Key features of our voice SMS & voice OTP platform
TTS + pre-recorded
Text-to-speech in Hindi and regional languages, or upload your own studio audio clips.
DTMF capture & IVR
Let recipients press 1 to confirm, pay or connect to an agent, captured as input.
Retry & AMD
Smart retry logic and answering-machine detection so codes reach a live listener.
Caller ID + scheduling
Present a registered caller ID/CLI and schedule broadcasts for the right time.
Real-time reports & webhooks
Live call status, DTMF and duration reports, pushed to your webhook endpoints.
Voice-OTP failover
Auto-trigger a voice OTP when SMS isn’t delivered for near-100% verification reach.
REST API
Trigger calls, TTS and OTP flows programmatically with clean, documented endpoints.
Connected-time billing
Pay only for connected talk time — unanswered and busy calls are never charged.
Voice Call API — developer integration
Trigger a voice OTP or alert call with a single REST request — pass TTS text or an audio URL, caller ID and language — then receive answered, DTMF, voicemail or failed events on your status webhook.
# Trigger a voice OTP call POST https://api.smsgatewayprovider.com/v1/voice/call Authorization: Bearer YOUR_API_KEY Content-Type: application/json { "to": "+919812345678", "caller_id": "09011XXXXXX", "language": "hi-IN", "tts": "Your OTP is 4 8 2 1. Press 1 to repeat.", "audio_url": null, "capture_dtmf": true, "retries": 2, "callback_url": "https://yourapp.com/voice/status" }
# Status webhook (POST to callback_url) { "call_id": "vc_7fa91c", "to": "+919812345678", "status": "answered", // answered | voicemail | failed | busy "dtmf": "1", "duration_sec": 12, "answered_by": "human", // human | machine (AMD) "billed_sec": 12 }
Only connected seconds are billed — voicemail and failed attempts cost nothing. See the full pricing for per-call and per-minute rates.
Voice OTP vs SMS OTP
Both channels verify users — the strongest setup uses SMS by default and voice as an automatic fallback.
| Dimension | Voice OTP | SMS OTP |
|---|---|---|
| Delivery speed | Rings and speaks in seconds | Fast, but can be queued or delayed |
| Success rate | High, even when text fails | High, drops on congestion/blocks |
| Offline/congestion reach | Connects on weak data networks and feature phones | May stall when SMSC is congested |
| SIM-swap resistance | Harder to intercept silently | Vulnerable to SIM-swap/redirection |
| Cost | Per connected call/minute | Per message |
| Best for | Fallback, feature phones, high-value verification | Default, high-volume verification |
Best practice: send an SMS OTP first and auto-trigger a voice OTP when it isn’t delivered.
Transactional vs promotional voice calls
Just like SMS, voice calls split into two categories under TRAI rules — and the compliance obligations differ.
Transactional / service voice
User-triggered OTPs, alerts, reminders and confirmations. These service calls carry lighter restrictions, can reach a user based on an existing relationship, and are the focus of this page.
Promotional voice (OBD)
Marketing broadcasts to opt-in audiences. These face DND/NDNC scrubbing, permitted 9 AM–9 PM hours and explicit consent. See promotional voice SMS.
Across both, we use TRAI-approved routes, a registered caller ID/CLI and DND scrubbing where required so your calls stay compliant.
Use cases by industry
BFSI
Voice OTP for logins and payments, plus fraud and suspicious-activity alerts.
Lending & NBFC
EMI and due-date reminders with press-1-to-pay or connect-to-agent DTMF.
Healthcare
Appointment and medication reminders that patients hear, not just read.
E-commerce & logistics
COD confirmation and delivery-window calls with press-1 to confirm the order.
Edtech
Class, fee and exam reminders in the student’s preferred language.
Government & utilities
Public alerts, scheme notifications and bill/outage reminders at scale.
A voice partner built for reach and reliability
Trusted by 5,000+ businesses across India and 190+ countries, with 15+ years in messaging — direct operator connects, honest billing and the reporting to prove delivery.
Near-100% OTP reach
SMS-to-voice failover means verification lands even when a text doesn’t.
Direct operator connects
Direct binds with Jio, Airtel, Vi and BSNL for clear, low-latency calls.
Connected-time billing
You pay only for answered talk time — never for busy or unanswered calls.
24×7 support
Human support any hour, plus 99.9% platform uptime for critical flows.
Voice SMS & voice OTP pricing
Voice is billed per connected call or per minute of talk time — unanswered, busy and voicemail attempts cost nothing. Rates depend on volume and destination, with lower slabs at higher monthly volumes; 18% GST applies in India.
See current per-call and per-minute slabs on our pricing page, or request a demo for a tailored quote.
