<!-- Source: https://docs.vinsi.ai/phone-connections/3cx -->
# Connect 3CX

Put a VINSI AI agent in front of your 3CX phone system — by forwarding calls, or with a SIP trunk for transfers to extensions.

Created: September 18, 2026

Updated: September 18, 2026

## Overview

3CX can hand calls to a VINSI AI agent in two ways. Most teams start with **call forwarding**, which takes minutes and needs no SIP configuration. If you need the AI to transfer callers to 3CX **extensions**, the two systems are linked with a SIP trunk through VINSI's Session Border Controller (SBC), set up together with the VINSI team.

## Choose a Route

|                    | Call forwarding                                                | SIP trunk through VINSI's SBC           |
| ------------------ | -------------------------------------------------------------- | --------------------------------------- |
| Setup              | Your 3CX admin, a few minutes                                  | VINSI and your 3CX admin together       |
| Calls in to the AI | Yes                                                            | Yes                                     |
| AI transfers to    | Full phone numbers (DIDs, ring groups or queues with a number) | 3CX extensions and phone numbers        |
| AI calls out using | A VINSI number                                                 | A VINSI number, or your 3CX lines       |
| Best for           | Getting started, and most receptionist setups                  | Transfers to many individual extensions |

## Route 1: Call Forwarding

### Set It Up

1. In VINSI, get a number for the agent (**Phone Numbers → Add Phone Number**) and assign it to the agent. See [Setting Up Phone Numbers](https://docs.vinsi.ai/ai-phone-agents/setting-up-phone-numbers).
2. In the 3CX admin console, set the inbound rule for the number callers dial — or the digital receptionist option you want the AI to handle — to forward to that VINSI number as an external number.
3. Call your main number from a mobile and check the AI answers.

Forwarded calls leave 3CX on one of your SIP trunk lines, so they count toward your trunk's simultaneous calls and your carrier's outbound minutes.

### Transfers Back to Your Team

The AI reaches your people by dialling a **full phone number**, not an extension. Give each transfer destination in your agent a number that rings in 3CX: a user's direct number, or a ring group or queue that has its own number.

**Don't transfer to the number that forwards to the AI.** The call would come straight back to the agent. Use a different number for transfers.

## Route 2: SIP Trunk Through VINSI's SBC

3CX connects to VINSI's SBC as a generic SIP trunk. The AI can then transfer to extensions by number — just the digits, 2 to 6 long — and, optionally, make outside calls through your own 3CX lines. This works the same way as the [Mitel connection](https://docs.vinsi.ai/phone-connections/mitel). Contact VINSI to set it up.

### What VINSI Needs From You

| Item                                                 | Notes                                                |
| ---------------------------------------------------- | ---------------------------------------------------- |
| Your 3CX public address                              | The FQDN or public IP of your 3CX, and its SIP port. |
| Extension range                                      | Which extensions the AI may reach.                   |
| Outside dialling format (if calling out through 3CX) | Any prefix your outbound rules expect.               |
| Caller ID to present                                 | The number recipients should see on outside calls.   |
| A test extension and a technical contact             | For the joint test.                                  |

### What Your 3CX Admin Configures

- A generic SIP trunk to VINSI's SBC (VINSI provides the address and sign-in details).
- An inbound rule on that trunk that delivers calls to the extension number that was dialled.
- Outbound rules that allow the calls you want the AI to make, if calling out through 3CX.
- Codec G.711 μ-law (PCMU) on the trunk.
- No SIP helper (SIP ALG) on the firewall in front of 3CX — it rewrites calls in flight and causes missing or one-way audio.

## Troubleshooting

| Problem                                         | Check                                                                                                             |
| ----------------------------------------------- | ----------------------------------------------------------------------------------------------------------------- |
| Forwarded calls don't reach the AI              | The forward target is the full VINSI number (e.g. +18005551234), and the number is assigned to an agent in VINSI. |
| Transfers loop back to the AI                   | The transfer destination is the forwarded number. Use a different number.                                         |
| The AI answers but doesn't recognise the caller | 3CX is replacing the caller's number on forwarded calls. Set the forwarding rule to pass the original caller ID.  |
| No audio or one-way audio (SIP trunk route)     | A firewall SIP helper is rewriting calls. Turn it off.                                                            |