how to build voice ai for inbound calls

You can have a Vapi agent answer every inbound call, ask qualifying questions, and hand the prospect off to Calendly to lock in a meeting - all without writing a single line of custom telephony code. The result is a self-contained voice AI agent that routes calls, captures lead data, and books calendar slots automatically. voice is the audible sound produced by a human speaker that can be captured, transmitted, and synthesized by software. voice AI agent is a software component that receives spoken input over a phone line, runs speech-to-text, applies a language model, and returns synthesized speech to the caller. Below you'll find everything you need to reproduce the exact workflow, from the required services to the n8n JSON that creates the Vapi agent, plus the pitfalls that usually bite new builders. What you need Tool Plan / Price Role Vapi Free tier or paid plan - check the Vapi pricing page Voice AI platform that hosts the conversational model and performs voice synthesis Twilio Pay-as-you-go voice minutes - check Twilio pricing Provides the inbound phone number and SIP termination for Vapi Calendly Free tier or paid plan - check Calendly pricing Calendar link generator and meeting scheduler n8n (self-hosted) Community edition - free (Docker) Orchestrates the webhook chain between Vapi, Twilio, and your CRM HubSpot CRM (optional) Free tier - check HubSpot pricing Stores qualified lead details for follow-up Estimated build time: 1-2 days for a minimal production-ready flow, assuming you already have accounts for the services above. how to build voice ai for inbound calls The core of the solution is a Vapi "agent" that runs a scripted dialogue, a Twilio phone number that forwards calls to Vapi, and an n8n workflow that receives the webhook payload, enriches the lead, and creates a Calendly event. Follow each numbered step precisely; the configuration values are written exactly as they appear in the UI. 1. Provision a Twilio phone number Log into the Twilio Conso