# Connect a FRITZ!Box with a SIP trunk

> Register a FRITZ!Box to the PBX with a SIP trunk so its phones can make and receive calls.

- URL: https://kb.voipcloud.online/teams-and-sip/sip-trunking/fritzbox/
- Section: Microsoft Teams and SIP trunking › SIP trunking
- Type: guide
- Applies to: Australia
- Last reviewed: 2026-11-09

This guide connects a FRITZ!Box router to your PBX with a SIP trunk, so phones plugged into or paired with the FRITZ!Box can make and receive calls on your number.

## Before you start

- Order a trunk licence and channels: go to **Services** › **SIP trunking**, set the number of **Channels** (one per simultaneous call), click **Add licence**, tick **Agree to service terms and conditions** and click **Submit order**.
- Have the FRITZ!Box admin password.

## 1. Create the SIP trunk in the PBX

1. Go to the **PBX** tab. Drag **SIP trunk** from the **Accept, make and divert calls** group onto the canvas and click the gear icon.
2. Enter a **Name** and set the **Number of channels**.
3. For **Mode**, choose **SIP registration**.
4. Choose a **SIP trunk call plan** and a **Caller ID** for outgoing calls.
5. Click **Save**.
6. Connect an [Inbound number](https://kb.voipcloud.online/pbx/receive-calls/inbound-number/) with your phone number to the SIP trunk.
7. Click **Apply configuration**.

Open the trunk's settings again and note the **SIP credentials**: **Domain**, **Username** and **Password**. Also note the **Transport protocol**: TCP, or TLS if **TLS encryption** is turned on in **Settings** › **General**. See [SIP trunk](https://kb.voipcloud.online/pbx/accept-make-divert/sip-trunk/) for every setting.

## 2. Add the number in the FRITZ!Box

**Note:** Menus can change between versions. If a label is different, check the vendor's own help.

1. Open the FRITZ!Box web interface and go to **Telephony** › **Telephone Numbers**. Add a new internet telephone number.
2. For the telephony provider, choose the **SIP Trunk** option if you see it. Otherwise, use the standard internet telephony option.

3. Fill in the number and account details:

 | FRITZ!Box field | Enter |
 | --- | --- |
 | **Telephone Number for Registration** | Your phone number with the area code. |
 | **Internal Telephone Number in the FRITZ!Box** | Your phone number without the area code. |
 | **User name** | The **Username**. |
 | **Password** | The **Password**. |
 | **Registrar** | The **Domain**, including the port. |

   ![FRITZ!Box Edit Telephone Number page with the number and account information fields](https://kb.voipcloud.online/images/teams-and-sip/sip-trunking/fritzbox-telephone-number.webp)

4. Under **Telephone Number Format**, set **Country code** to **None**, and set **Area code** to **With prefix (0X)**, where X is your area code. For example, **With prefix (07)** for a Queensland number.

   ![Telephone Number Format with Country code set to None and Area code With prefix](https://kb.voipcloud.online/images/teams-and-sip/sip-trunking/fritzbox-number-format.webp)

5. Leave the other settings as they are and click **OK**.

If your FRITZ!Box has a transport setting for the number, set it to match the trunk's **Transport protocol** in the PBX (TCP, or TLS).

## Check it works

1. In the PBX, the SIP trunk's **Status** shows **Online**.
2. Call your number from a mobile. The phone on the FRITZ!Box should ring.
3. Call a mobile from that phone. The mobile should show your caller ID.

If the trunk stays offline, check the user name, password and registrar: after failed sign-in attempts, the PBX blocks the IP address for 5 minutes. You can check this with **Check IP address for blocking** in the trunk's settings.

## Next steps

- [Device offline](https://kb.voipcloud.online/troubleshooting/device-offline/) if the FRITZ!Box won't register.