The Trunks service setting template provides for the creation of custom outbound Caller ID settings "Service Numbers" to be applied to users

The Process

Service Numbers are configured separately to Trunk Number Ranges and are normally used for presenting a common outbound number for a group function, such as:

  • Presenting a common number for the entire company on outbound calls
  • Providing a group number where for example the helpdesk users will present the customer support number when they call out
  • Allowing a user to present their assistant's number so returned calls are screened
  • Your company uses a non-geographic number that is not directly carried by your Trunk provider
  • The company main number is on one trunk service but the company uses several trunk providers

Adding Trunk Number Ranges

One or several Trunk Number Ranges can be added to a trunk profile. These number ranges will be provided by the SIP Trunk service provider.

A trunk range may be a single number

Add the ranges using the +Add/Edit Number  facility for Trunk Number Ranges. This will open a window to manage the Trunk Number ranges.

When adding numbers, the full E164 number without spaces or any special characters, should be added for the start and end range. Find out more about E164 numbers in this article.

Trunk Number Ranges can be managed and ranges added and deleted. Existing ranges cannot be deleted if attached to a user. A Trunk Number Range cannot be modified, it should be deleted and re-added with the revised settings.

Once added the portal will provide summary information of the Trunk numbers available

Creating Service Numbers

Several Service Numbers can be created using the +Add/Edit Number  facility for Service Numbers. This will open a window to manage the Service Numbers


Only add service numbers which your service provider allows you to use for Caller ID. Presenting numbers that are you are not authorized to, is in contravention of the service usage terms and in some cases may be unlawful.  It is likely that your service provider will block numbers that you are not authorized to use, so incorrectly setting the Service Number may cause a service unavailability.

Add the service numbers in the portal and also provide the Display Name. The Display Name is transmitted with the outbound call and on certain networks will reach the called party. The Display Name is also used when managing users.

Ensure the Service Number is provided on E164 format (starting with a '+', no leading zero), then the country number and without spaces or other separators.

Service Numbers can be managed and ranges added modified and deleted. Existing numbers cannot be deleted if attached to a user.

Summary information regarding Service Numbers will be displayed in the portal:

E614 manipulation applies to Service Numbers so if the trunk profile has E164 manipulation settings then this will modify outbound numbers in the same way as regular outbound calls.


The selection of Service Numbers are those associated with the Trunk profile, If you want users on several different trunks to present the same Service number, the Service Number should be defined on each trunk.

Managing Service Numbers for Users

In the 'Add-users' section of the portal, an additional field is available for Trunk users to select the outbound Caller ID

For each user, you can select:

  • The outbound caller ID will be their Trunk Number or DiD (default)
  • Outbound calls will show as anonymous
  • A Service number will be presented for calls made by the user.

The same Service Number can be applied to multiple users

Working with Few Trunk Numbers for Many Users

Each user will need a trunk number assigned to allow the service to operate. In the situation where the Trunk provider may only provide one or a few numbers, an additional range should be created to apply to all users. In this scenario a main number would typically be connected to an Auto Attendant or Call Queue.

Along with the short number ranges provided by your trunk provider, add a 'dummy' number range can be used for users. Ensure these numbers are not in the pattern of any PSTN number that may be dialled, and at least 7 digits in length. The numbers will also need to be formatted as E164 numbers  (starting with a '+', no leading zero).

Apply numbers from the dummy range, to each user and set their outbound Caller ID.  The dummy trunk number will be displayed in the user's Teams client as thier number, but this is purely for display proposes as their outbound number is set by the portal Users will be calling each other by name so the number is not used otherwise.

Technical Notes

From Header Settings

The service number setting applies to the From header passed to the Trunk provider. Ensure that the 'From Header' and the 'P-Asserted-Identity Header' are set to reflect the desired behaviour. 

Setting the From Header setting to be the Trunk User Number (default) to pass the modified caller Id to the Trunk provider. Optionally setting the P-Asserted-Identity Header to the Trunk User Number (default) will send the user's DiD to the Trunk provider for billing purposes.

Inbound Caller ID.

We will pass through what we receive. If the Caller ID contains details of the caller in text format these are passed. However, if, upon receipt, the Teams client matches the number to an entry in the Teams Contacts or Azure AD, the corresponding entry may be displayed. We have no control over this and are fully dependent on the Caller ID that is presented in the SIP headers received. To understand how Teams handles this, please refer to this article: Reverse Number Lookup - Microsoft Teams