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    AI Voice Assistant

    A real-time AI voice calling system where users call a phone number (or use a browser) and have a natural conversation with an AI agent. Uses Twilio for call handling, OpenAI Whisper for speech-to-text, GPT-4o for reasoning, and a TTS engine for voice synthesis. Latency under 1.5 seconds.

    100 – 10Kusers supported
    $300 – $5,000/month infrastructure

    Architecture Diagram

    Interactive — hover over any node to see its role and description.

    Phone / WebTwilio SDKTwilioVoice APIVoice ServerNode.js WSWhisper STTOpenAIGPT-4oLLM ReasoningTTS EngineOpenAI / ElevenLabsPostgreSQLRedis CacheUserExternalBackendAI / MLDatabaseCache

    Use Cases

    AI receptionist for inbound sales calls
    Automated appointment booking and reminders
    AI-powered customer support hotline
    Voice-based lead qualification system
    Interactive voice response (IVR) replacement

    Technology Stack

    frontend

    ReactWebRTCTwilio Voice SDK

    backend

    Node.jsWebSocketExpress

    database

    PostgreSQLRedis

    infrastructure

    AWS EC2DockerNginx

    ai

    OpenAI Whisper (STT)GPT-4oOpenAI TTSElevenLabs (premium TTS)

    integrations

    Twilio Voice APICalendar APIsCRM Webhooks

    Scalability Roadmap

    Stage 10 – 100 users· Single EC2 c5.large

    Single compute-optimised EC2. Handles ~20 concurrent calls. Twilio pays per minute — no upfront cost.

    Stage 2100 – 1K users· EC2 Auto Scaling + ElastiCache

    Multiple voice server instances with sticky sessions. Redis cluster for shared call state.

    Stage 31K – 10K users· ECS + Aurora + Custom STT

    ECS for dynamic scaling. Consider self-hosted Whisper for cost reduction at high call volumes.

    Stage 410K+ users· Global PoPs + dedicated STT clusters

    Regional deployments for low latency. Dedicated GPU clusters for STT/TTS. Custom fine-tuned voice models.

    Cost Breakdown

    Development Cost

    $20,000 – $50,000 (10–20 weeks)

    Infrastructure Cost

    $300 – $5,000/month (Twilio per-minute + OpenAI API are variable costs)

    Maintenance Cost

    $2,000 – $6,000/month for latency tuning, voice model improvements, and compliance

    Security Considerations

    All calls recorded and stored encrypted — with caller consent notice
    Twilio BYOC (Bring Your Own Carrier) for number ownership and portability
    Conversation transcripts scrubbed for PII before logging
    Per-call JWT tokens preventing replay attacks on webhook endpoints
    TCPA compliance: do-not-call list integration and call time restrictions

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