You can add an AI voice agent to 3CX in two ways. The first is 3CX's own AI Receptionist, which needs the 3CX AI Edition and your own OpenAI account. The second is to register an external AI agent as a Generic SIP Trunk in 3CX and route chosen calls to it from your digital receptionist or an inbound rule. The second route takes about 20 minutes and is the one to use when you need the AI to resolve calls, take actions in your systems, and create a ticket in your helpdesk for every call.
This guide covers both, then walks through the SIP trunk setup step by step.
TL;DR
- 3CX AI Receptionist is built in, needs the AI Edition licence, and runs on your own paid OpenAI API account. 3CX says each AI call is capped at 3 minutes, which suits greeting and routing more than full resolution.
- An external AI agent connects as a Generic SIP Trunk. Your extensions, ring groups, queues, recordings and digital receptionist stay in 3CX.
- Setup order: create the SIP trunk in 3CX, point one digital receptionist option or DID rule at it, add the same numbers in the AI platform, test.
- Helpdesk logging happens on the AI side: the agent creates a ticket with the transcript and outcome in Zendesk, Freshdesk, HubSpot, Salesforce or Intercom.
- Handoffs go back to a 3CX queue, ring group or extension with SIP REFER, with the transcript attached.
- Cost: your 3CX licence and PSTN carrier stay the same. Open adds $0.75 to $0.90 per resolved call, and handoffs to humans are not billed.
Option 1: 3CX's built-in AI Receptionist
3CX added an AI Receptionist to its phone system. 3CX describes it as answering and routing calls, screening spam, taking messages and capturing caller details, powered by OpenAI. You configure it in the 3CX Admin Console: connect your OpenAI account, create an AI agent, assign it to an extension and describe its behaviour. You can choose the voice, accent and language.
What to know before you choose it:
- Licence. The receptionist requires the 3CX AI Edition. A GetVoIP review published in October 2026 notes that the licence does not include a bundle of AI minutes.
- Model costs. You need a paid OpenAI API account with credit. 3CX suggests setting usage budgets in OpenAI's dashboard to keep costs predictable, which also means AI usage is a second bill to watch.
- Call length. 3CX's own FAQ states a maximum of 3 minutes per AI call. That is fine for "who are you and where should I send you", short for "reschedule my delivery and update the address".
- Actions and knowledge. Uploaded knowledge covers static answers like opening hours and policies. Independent reviewers could not confirm which CRM or helpdesk actions the built-in receptionist performs on its own.
When it is the right choice: you want a smarter front door that answers 24/7, screens calls and sends them to the right person, and you are happy to keep resolution with your team. For a small office on the AI Edition already, it is the quickest win.
Option 2: an external AI agent over a 3CX SIP trunk
The other approach treats the AI agent like any other SIP endpoint. 3CX handles standard SIP trunks well, so an AI platform can register as a Generic SIP Trunk without custom modules. Your 3CX setup stays as it is. You decide which calls go to the AI: one digital receptionist option, after-hours calls, overflow from a queue, or a whole DID.
This is how Open connects to 3CX. It works the same on self-hosted 3CX and on 3CX-hosted plans, and the AI can do things mid-call (look up an order, book a slot, create a ticket) because it connects to your tools directly. When it needs a human, it warm-transfers back into 3CX.
Built-in vs external: side by side
| 3CX AI Receptionist | External AI agent via SIP trunk (e.g. Open) | |
|---|---|---|
| Licence needed | 3CX AI Edition | Any 3CX edition that supports SIP trunks |
| AI model costs | Your own OpenAI API account, billed separately | Included in the per-resolution price |
| Max call length | 3 minutes per AI call (3CX FAQ) | Not subject to 3CX's AI call cap |
| Main job | Greet, screen, route, take messages | Resolve the call, take actions, then route if needed |
| Helpdesk logging | Not documented for the built-in receptionist | Creates a ticket with transcript and outcome |
| Handoff | Fallback routing to an agent or voicemail | Warm transfer by SIP REFER with transcript |
| Setup | Admin Console plus OpenAI configuration | About 20 minutes: SIP trunk plus one routing rule |
| Best for | Small offices that want a smarter front door | Support teams that want calls resolved and logged |
How to connect an AI voice agent to 3CX: step by step
These steps follow Open's 3CX integration guide. Other AI platforms that connect over SIP will look similar, though menu names on their side will differ.
Before you start
- Admin access to the 3CX Management Console.
- At least one DID you want the AI to answer, or a digital receptionist option you want to hand to the AI.
- A decision on scope: start with one branch, such as after-hours calls or "press 2 for order status", rather than every call.
Part A: inbound calls
- Open the SIP settings in your AI platform. In Open, that is Settings, then SIP, then the inbound trunk configuration.
- Pick a SIP region. Choose Global, US, EU or APAC. Pick the one closest to your 3CX server and your callers to keep latency down.
- Copy the SIP credentials. You need the SIP endpoint, a username and a password.
- Add a SIP trunk in 3CX. In the 3CX Management Console, go to SIP Trunks, then Add SIP Trunk, then Generic SIP Trunk. Enter the AI platform's SIP host and the credentials from step 3. Use TLS for production traffic.
- Choose the branch to automate. Decide which digital receptionist option or inbound rule should reach the AI.
- Route that branch to the trunk. Set the branch's destination to the new SIP trunk, or to a virtual extension that forwards to it. Everything not routed there keeps working exactly as before.
- Add the matching numbers in the AI platform. In Open, add the 3CX DIDs that front that branch under Phone Number (DID).
- Assign the numbers to an AI agent. In Open, go to Channels, Phone, Agents, and assign the DIDs.
- Place a test call. Dial the 3CX number, take the AI branch, and confirm the agent answers. 3CX call recording and reporting still see the call leg.
Open's guide estimates 15 to 20 minutes for inbound once the trunk registers.
Part B: outbound calls (optional)
If the AI should also place calls, such as callbacks or reminders:
- Add an outbound trunk in the AI platform that points at your 3CX server's FQDN on port 5060, or TLS.
- Paste the SIP trunk username and password from 3CX for digest authentication.
- Set a caller ID you have outbound rules for in 3CX.
- Assign the trunk to the agent that should use it.
Your 3CX outbound rules still decide which calls are allowed and which caller ID is shown.
How to log every call to your helpdesk
A 3CX call log tells you a call happened. A helpdesk ticket tells you why the customer called, what was done, and whether it is closed. To get the second, the logging has to happen where the conversation is understood, which is on the AI side.
- Connect your helpdesk to the AI platform. Open connects to Zendesk, Freshdesk, HubSpot, Salesforce, Intercom and Twilio Flex, or you can use Open's own helpdesk.
- Add ticket creation as an action. Configure the agent to create a ticket on every call, not only on escalations. Include the caller's number, the transcript, the detected intent and the outcome (resolved, handed off, callback needed).
- Match the caller to a customer record. If your CRM or helpdesk holds phone numbers, have the agent look the caller up at the start of the call so the ticket lands on the right contact.
- Tag by outcome. Use tags or fields for "resolved by AI" and "handed to human". These make it easy to report automation rate in the helpdesk your team already uses.
- On handoff, pass context both ways. When the AI transfers to a 3CX queue or extension, the person who picks up gets the transcript and intent. The ticket is already open, so they update it instead of creating a duplicate.
Check field mapping with a few test calls before going live. The most common problem is tickets created without a requester because the caller's number format (with or without the country code) does not match the helpdesk record.
What it costs
- 3CX: your licence and hosting fees do not change. 3CX licences are priced per system per year, by simultaneous calls, rather than per user.
- PSTN carrier: whatever SIP provider gives you phone lines today keeps billing its minutes.
- The AI agent: Open charges $0.75 to $0.90 per resolution, depending on volume. Calls handed to a human are not billed, and carrier and telephony costs are passed through at cost. Full details are on the pricing page.
With the built-in receptionist, the equivalent costs are the AI Edition licence plus your OpenAI API usage.
Common problems and fixes
- Trunk will not register. Check that the AI platform's SIP host is reachable from your 3CX server and that the firewall allows SIP and RTP. If you use IP allowlisting instead of credentials, confirm both sides have the right public IPs.
- One-way or no audio. Usually NAT or RTP ports. Check 3CX's firewall checker and the RTP port range.
- AI answers but the wrong agent picks up. The DID added in the AI platform must match the number 3CX forwards, in the same format.
- Transfers fail. Confirm the 3CX trunk accepts SIP REFER, and that the target queue or extension exists.
Where to go next
If you mostly need a polite front door, start with the 3CX AI Receptionist. If you need calls resolved and every one of them logged as a ticket, connect an external agent over a SIP trunk. Open's AI receptionist can look callers up in your CRM, book appointments, create tickets and hand off warmly, and the same setup pattern works across other phone systems if you run more than one.
Sources
- 3CX, AI Receptionist, https://www.3cx.com/phone-system/ai-receptionist/, checked 2026-11-12
- GetVoIP, 3CX AI Receptionist review (1 October 2026), https://getvoip.com/blog/3cx-ai-receptionist-review/, checked 2026-11-12
- 3CX, Annual pricing, https://www.3cx.com/ordering/pricing/, checked 2026-11-12
- Open, AI phone agent on 3CX, https://www.open.cx/telephony/3cx, checked 2026-11-12
- Open pricing, https://www.open.cx/pricing, checked 2026-11-12