Step-by-step guide to connecting an AI receptionist to your 3CX phone system via SIP trunk.
No more keypad menus. In this article we walk through the full configuration — 3CX users, queues, SIP trunk, AI agent with transfer rules — so callers talk to an AI that actually routes them to the right department.
We all know them — Interactive Voice Response menus. When you call your bank or ISP, you navigate at least one (often four nested) menus. Listening carefully for options, picking the closest match, and starting over when you misclick.
Modern AI Voice Agents support natural language and can integrate into your phone system via SIP — perfect for 3CX. We start by building the AI agent, then configure 3CX to route calls correctly.
3CX is a leading open-standard IP PBX with a full unified-communications suite — calls, video, live chat, all from one platform. For this project you need the self-hosted or private-cloud version, as custom SIP providers are unsupported on 3CX's own cloud.
AI Voice Agents hold natural conversations, understand context, and act on user input. Instead of rigid menus they respond dynamically. ElevenLabs Conversational AI and Retell.ai are the two market leaders that ship with SIP integration out of the box.
For private-cloud hosting, 3CX runs comfortably on a small VPS at Vultr, Hetzner or DigitalOcean — from €5/month.
Follow these in order. Don't skip — some depend on earlier ones.
Start in the 3CX Admin panel. We create the people who answer phones, the queues the AI routes to, and the SIP trunk that connects 3CX to the AI.
ElevenLabs only accepts E.164-formatted traffic. For tests use fictional numbers reserved for demos. The + in the prepend is mandatory — without it the call never connects.
Log into your ElevenLabs or Retell account → Conversational AI → Agents → New Agent. Start with a Business Agent template, customize the System Prompt for your business, then enable the Transfer tool and link each department to a 3CX queue.
# Personality
Je bent Celia, een professionele en efficiënte receptioniste voor {{business_name}}. Je bent vriendelijk, helder en behulpzaam, en zorgt dat alle bellers bij de juiste afdeling uitkomen.
# Environment
Je beantwoordt telefoongesprekken voor {{business_name}}. Bellers zijn extern en willen mogelijk Sales, Boekhouding, of Support bereiken.
# Tone
Je antwoorden zijn warm, hoffelijk en vriendelijk — maar kort. Vermijd jargon. Spreek in een normaal tempo en articuleer duidelijk.
# Goal
Je primaire doel is binnenkomende gesprekken efficient naar de juiste afdeling te leiden.
1. Begroeting: "Goedendag, met {{business_name}}, met wie wilt u worden doorverbonden?"
2. Information Gathering: Identificeer welke afdeling de beller nodig heeft (Sales, Boekhouding, Support). Bij twijfel: stel verhelderende vragen.
3. Confirmation: "Dus u wilt naar {{department}}? Een moment, ik verbind u door."
Verbind direct door via de Transfer to Number tool.
# Guardrails
Geef geen informatie over financien, interne policies, of medewerkers buiten publieke directory info.
Bij agressieve bellers: beleefd afbreken.
# Tools
- End Call
- Transfer to Number (SIP REFER)Sample System Prompt — adapt '{{business_name}}' and department names.
Pick a quality voice (e.g. ElevenLabs Multilingual v2 with a regional accent). Callers can hear the difference between Multilingual v2 and cheaper TTS immediately.
Time to wire the two sides together. On the AI platform side we configure incoming SIP; in 3CX we ensure the outbound rule matches.
Match the + and number EXACTLY between the 3CX outbound rule and the ElevenLabs phone number. A one-character difference and your call never lands.
From a 3CX extension dial the number you configured for the AI. You should hear the AI ask where to route your call. Test every department.
Don't route ALL inbound calls to the AI at once — start with after-hours or lunch to limit risk. Scale up as confidence grows.
Issues I hit during the first rollout — and how to fix them.
Fix: Check you added the '+' in the prepend section of your outbound rule, and that the numbers match exactly between 3CX outbound rules and the ElevenLabs Phone Numbers config.
Fix: Make sure 'Include diversion header support' is enabled on your ElevenLabs SIP trunk. Also check the queue extension numbers in your Human Transfer Rules match those in 3CX.
Fix: Ensure 'Transfer to Number' is enabled in the agent's Tools section. In your System Prompt, explicitly tell the agent it can transfer directly without reading numbers aloud.
Fix: Try Media Encryption set to 'Allowed' (not 'Required') on both sides. Verify your 3CX server has enough bandwidth for the codec (G.711 minimum).
Fix: Increase boosted_keywords in the agent config with industry-specific terms. Keep voice_temperature low (0.3-0.5) for more consistent answers.
We offer telephony consulting for businesses replacing their IVR with AI — from 3CX setup to SIP trunking to AI agent training. Book an intake and we deliver within 2 business days.