> ## Documentation Index > Fetch the complete documentation index at: https://www.vobiz.ai/docs/llms.txt > Use this file to discover all available pages before exploring further. # What Is an AI Phone System? Features, Cost & How to Build One > An AI phone system replaces a traditional PBX with an AI voice agent that answers calls, routes them intelligently, books appointments, and handles customer queries — no hardware, no hold queues. How it works, what it costs, and how to set one up on Vobiz. *November 2026 · Vobiz Team* **An AI phone system is what happens when you replace a traditional PBX and IVR with a conversational AI agent that actually understands what callers say.** Instead of "Press 1 for Sales, Press 2 for Support", callers say "I need to check my invoice" and the AI routes them, looks up their account, and either resolves it or connects them to billing — all in under 2 seconds. > [!NOTE] > > **Key takeaways** > > * AI phone systems replace rigid IVR menus with open-ended conversational routing > * No hardware required — runs entirely in the cloud (Vobiz telephony + AI agent platform) > * Answers 24/7, handles unlimited concurrent calls, books appointments, and routes by intent > * Cost for a small business: ₹5,000–15,000/month vs ₹25,000–40,000/month for a human receptionist > * Indian numbers, Hindi/regional language support, and TRAI compliance built into Vobiz ## AI Phone System vs Traditional PBX | Feature | Traditional PBX | AI Phone System | | - | - | - | | **Hardware** | On-premise server box | None — fully cloud | | **Call routing** | Extension numbers + IVR menus | Natural language intent | | **Menu navigation** | "Press 1, Press 2…" | "I'd like to speak to billing" | | **24/7 coverage** | Voicemail after hours | AI answers and handles 24/7 | | **Appointment booking** | Manual (agent books) | AI books via calendar API | | **CRM integration** | Manual lookup | Real-time API during call | | **Multiple languages** | Pre-recorded only | Live multilingual AI | | **Scalability** | Add physical lines | Instant — elastic channels | | **Setup time** | Days to weeks | Hours | | **Maintenance** | IT team required | None | ## What an AI Phone System Does **Answers every call instantly**: No hold music, no unanswered calls during peak hours. The AI agent picks up within 2 rings. **Understands natural language routing**: "I want to know about my EMI due date" routes to billing. "I'd like to reschedule my appointment" triggers the booking flow. The AI understands intent, not just keywords. **Books and manages appointments**: Connects to your calendar in real time. Checks availability, offers slots, confirms the booking, sends SMS confirmation. **Answers FAQs from a knowledge base**: Business hours, pricing, office location, return policy, product information — all answered instantly from a configured knowledge base. **Looks up customer data live**: When a customer calls, the AI queries your CRM with their phone number and reads back their account status, order status, or balance — no "can you tell me your account number" delay. **Transfers with context**: When escalating to a human, the AI summarises the call: "Transferring to billing. Customer is asking about invoice #4521 from October, believes there's an overcharge." The human agent starts informed. **Handles after-hours**: Outside business hours, the AI continues to book appointments, answer FAQs, and take messages — with a note that a human will follow up on the next business day. **Makes outbound calls**: Beyond inbound, an AI phone system can initiate calls for appointment reminders, payment alerts, order updates, and surveys. ## Components of an AI Phone System ``` Phone Number (Vobiz) ↓ SIP Trunk (Vobiz) ↓ AI Voice Agent Platform ├── ASR: Deepgram / Sarvam / Google STT ├── LLM: GPT-4o / Gemini / Claude └── TTS: ElevenLabs / OpenAI / Sarvam ↓ Integrations ├── Calendar API (appointments) ├── CRM API (customer data) └── Webhook (call logging) ↓ Human Agent (escalations only) ``` ## Setting Up an AI Phone System on Vobiz **Step 1: Get your business number** In [Vobiz Console](https://console.vobiz.ai), buy a phone number. Options: * **10-digit mobile number** — standard Indian business number * **140-series** — required for B2C outbound; also works for inbound * **1800 toll-free** — for businesses where callers shouldn't pay * **International DID** — if you serve global customers **Step 2: Choose your AI agent platform** | Platform | Best for | Effort to set up | | - | - | - | | **Retell AI** | No-code, quick launch | Low | | **Vapi** | Developer control, function calling | Medium | | **ElevenLabs** | Premium voice quality | Low | | **Custom (Python + Pipecat)** | Full control, custom ASR/LLM/TTS | High | **Step 3: Write your agent prompt** The system prompt defines your AI phone system's behaviour: ``` You are [Name], the AI receptionist for [Business Name]. Business hours: Monday–Saturday, 9am–6pm IST. Languages: English and Hindi. When someone calls, greet them and ask how you can help. You can: 1. Answer FAQs about our products/services 2. Book appointments (call the /book-appointment API with date and time) 3. Look up order status (call the /order-status API with phone number) 4. Transfer to a human agent (say "Let me connect you to our team") Transfer to human if: - The caller is frustrated or upset - The query involves a refund > ₹2,000 - The caller explicitly asks for a human Always be polite, brief, and helpful. ``` **Step 4: Connect SIP trunk** Create an inbound SIP trunk on Vobiz → set the origination URI to your AI platform's SIP address → link your phone number to the trunk. For platforms using WebSocket (Pipecat, custom agents), use Vobiz's XML streaming: return `` verb pointing to your WebSocket endpoint. **Step 5: Configure integrations** Point the agent to your calendar API and CRM endpoint. Test by calling your Vobiz number and working through each scenario: FAQ, appointment booking, order lookup, escalation. Detailed guides: * [Retell AI dashboard setup](https://www.vobiz.ai/docs/integrations/retellai-dashboard.md) * [Vapi dashboard setup](https://www.vobiz.ai/docs/integrations/vapi-dashboard.md) * [ElevenLabs setup](https://www.vobiz.ai/docs/integrations/elevenlabs-dashboard.md) ## AI Phone System for Different Business Types **Small business / solo professional** A single Vobiz number with a Retell AI or Vapi agent. Answers calls when you're unavailable, books appointments into your Google Calendar, takes messages. Cost: ₹2,000–5,000/month. **Medical clinic** Multi-line setup with patient routing. "Press 1 for appointments, 2 for prescriptions, 3 for the lab." AI books appointments, reads out lab results, routes urgent calls to the duty doctor. Full HIPAA/data-handling consideration for sensitive patient data. **E-commerce / D2C brand** Inbound customer service: order status lookup, return initiation, delivery queries. AI resolves 70%+ of calls; escalates only disputes and complex cases. Integrates with Shopify, WooCommerce, or custom order APIs. **Financial services / NBFC** EMI reminder outbound calling, inbound query handling (balance, next EMI date, payment options). 140-series caller ID, TRAI compliance, encrypted call recording. **Real estate agency** Inbound enquiries from property listings: AI reads property details, qualifies buyer interest, books site visit appointments, routes qualified leads to agents. ## Cost Model | Component | Monthly Cost | | - | - | | Vobiz phone number | ₹200–500 | | Vobiz inbound minutes (3,000 min) | ₹600–1,350 | | AI platform (Retell/Vapi) | ₹2,000–8,000 | | LLM + TTS inference | ₹1,000–4,000 | | **Total** | **₹3,800–13,850/month** | Compare to a human receptionist: ₹25,000–40,000/month in salary alone. For businesses receiving 50+ calls per day, an AI phone system pays for itself within weeks. ## Next Steps * [Create a Vobiz account](https://console.vobiz.ai) and buy your business phone number * [Read the AI receptionist guide](https://www.vobiz.ai/docs/blogs/what-is-an-ai-receptionist.md) for a full setup walkthrough * [Connect Retell AI](https://www.vobiz.ai/docs/integrations/retellai-dashboard.md) for a no-code start * [Explore the AI voice agent guide](https://www.vobiz.ai/docs/solutions/ai-voice-agent.md) for custom pipeline architecture This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.