An autonomous AI voice agent built with Vapi, ElevenLabs, and OpenAI GPT-4o to handle 24/7 inbound enquiries, lead qualification, and calendar bookings for a UK service business — replacing a manual intake bottleneck and answering 100% of out-of-hours calls with zero human intervention.
A UK service business was losing high-intent customer leads during evenings, weekends, and peak operational hours due to missed inbound phone calls. With no budget for a 24/7 dedicated reception team, manual callback attempts suffered from high drop-off rates and lost revenue to competitors who answered immediately.
Instant pickup within two rings on all inbound business lines with zero wait times or dropped calls
Sub-800ms voice roundtrip with dynamic interruption handling for natural human-like conversations
Context-aware inquiry triage, caller intent extraction, and strict business rule validation
Real-time slot availability checking, instant appointment booking, and automatic CRM activity logging
Dynamic SIP call bridging to on-duty team members when high-value VIP or emergency criteria are met
PSI Square engineered an autonomous voice agent using Vapi for sub-second orchestration, ElevenLabs for natural voice synthesis, OpenAI GPT-4o for conversational intelligence, and an n8n webhook pipeline connecting directly to HubSpot CRM and Google Calendar.
Vapi + ElevenLabs + GPT-4o
Custom-tuned ElevenLabs voice clone paired with Deepgram Nova-2 speech recognition for sub-second, crystal-clear natural speech.
OpenAI GPT-4o processes caller inquiries with custom prompt guards, company FAQ ingestion, and real-time structured function calling.
Advanced voice activity detection (VAD) allows callers to interrupt naturally mid-sentence without jarring robotic speech overlaps.
Twilio + n8n + HubSpot
Twilio SIP trunk routing connects existing local business lines directly to the voice orchestrator with carrier-grade uptime.
Automated webhook triggers fetch real-time calendar availability, book appointments, and generate instant summary notifications.
Call transcripts, audio recordings, structured qualification tags, and contact records automatically logged to HubSpot CRM.
Production telemetry and component specifications for high-reliability telephony, sub-second LLM reasoning, and automated CRM logging.
Measured call completion rates and operational triage performance validated across live production caller volume.
Within the first month of deployment, the AI voice agent answered 100% of inbound calls outside regular business hours, completely eliminating missed-call lead loss. Over 70% of inbound callers were successfully qualified and booked directly into the team calendar without any manual staff involvement. The business scaled inquiry volume without increasing reception payroll.
We build custom autonomous AI agents, voice receptionists, and enterprise webhook integrations.
Tell us about your call handling challenge. We'll scope it, design it and deliver it to production standard.
Or email info@psi-square.net · Phone +44 (0) 20 3872 7195 · We reply within 24 hours · NDA available on request
