Every invite, in a human voice
Sparkstream Technology LLP · March 2026
Divyang Jain · Harsh R Jain
Your 500-guest wedding deserves better than a group forward that gets muted
Calling 200 people takes a full week and your phone battery. Nobody does it.
Cold, voiceless text blasts. Nobody reads promotional SMS anymore.
Name your campaign. Pick English or Hindi language.
Choose a DLT template or write custom. Use {name}, {date}, {venue}.
Drop a CSV with name + phone columns. Contacts parsed instantly.
Watch calls go out in real-time. Per-contact status dashboard.
Safety: GPT-4o-mini content validator ensures no harmful messages go out. Gemini 2.0 Flash as fallback.
| Layer | Technology | Purpose |
|---|---|---|
| English TTS | ElevenLabs Flash v2.5 | Photorealistic voice, $0.15/1K chars |
| Indian TTS (10 langs) | Sarvam AI bulbul:v2 | Native accent, 8 kHz telephony |
| Telephony | VoBiz + Exotel + Twilio | India-first call routing, webhook status |
| Voice Clone | ElevenLabs Instant Clone | 30-second sample to AI voice |
| Content Safety | GPT-4o-mini + Gemini 2.0 | LLM validates every message |
| Storage | AWS S3 (ap-south-1) | Pre-gen WAV files, CDN delivery |
| Payments | Razorpay | UPI, cards, net banking (INR) |
| Backend | FastAPI + PostgreSQL | Async Python, Alembic migrations |
| Frontend | React + Vite + Tailwind | Mobile-responsive SPA |
Technical moat: Pre-generated 8 kHz WAV files cached in S3. Calls connect with zero latency on playback.
11 Languages Live
Sarvam AI + ElevenLabs powering all 11 languages
60+ DLT-verified templates across wedding, event, reminder, festival, and business -- in 11 Indian and English languages
Unique audio generated for each person
Campaign-level variables, same for all contacts
Example Call Script
"Hello Priya, you are cordially invited to our wedding on the 15th of March at The Grand Ballroom. We would be honoured by your presence."
| Contact | Status | Duration |
|---|---|---|
| Rohan Sharma | Answered | 32s |
| Priya Mehta | Answered | 28s |
| Anil Gupta | Calling | -- |
| Sunita Rao | No Answer | -- |
| Vijay Patel | Answered | 45s |
| Meena Joshi | Failed | -- |
Full audit trail: call SID, status, duration, timestamp per attempt. Unanswered calls can be retried at no extra charge.
Record or upload a 30-second audio clip of your voice
ElevenLabs Instant Clone creates your personal voice model
Every guest hears YOU -- not a generic AI. That's the magic.
Unit cost per EN call: ~$0.034. Starter worst-case margin: 63%. Actual margin (mixed Hindi/static): 75-80%.
| Feature | onvoice | Exotel Studio | Twilio (DIY) | Legacy IVR |
|---|---|---|---|---|
| Multi-language TTS | 11 languages | -- | -- | Partial |
| Per-contact personalization | Yes | -- | DIY only | -- |
| Voice cloning | Yes | -- | -- | -- |
| DLT templates | Yes | -- | -- | SMS only |
| No-code wizard | Yes | -- | -- | -- |
| India pricing | From INR 749 | INR 10K+ | Dev cost | INR 20K+ |
| Self-serve signup | Yes | Sales-only | Yes | Sales-only |
Exotel and Twilio are plumbing. onvoice is the finished product. We are the Stripe Checkout of voice calls.
"I called all 300 wedding guests in a single afternoon.
Half of them thought it was actually me calling."
Early user, February 2026
Built and shipped by a 2-person team. 100% uptime on production telephony integrations.
Marketing strategy and India market expertise. Leads brand positioning, go-to-market execution, and growth for onvoice. Deep understanding of Indian consumer behavior and communication patterns.
MS in Machine Learning & AI. Full-stack engineering, system architecture, and AI/ML integration. Built the entire onvoice platform from TTS pipeline to telephony orchestration to production deployment.
"We built onvoice because we tried to invite people to a friend's wedding, and realised there was no good way to do it."
Sparkstream Technology LLP
Here's what we'll do with it
Voice is the most human channel. AI has made it affordable.
India is the biggest opportunity. We are the only team building this.
Now is the time.