Applies To

Call2Teams - Customers



This article covers setting up Trunks and creating custom outbound Caller ID (Presentation ID) settings.

Service Numbers

Service Numbers are configured separately to Trunk Number Ranges.

Service Numbers can be used for presenting a common outbound number for a group function, such as:

  • Presenting a common number for an entire company on outbound calls
  • Providing a group number such as a customer support number for helpdesk users to present on outbound calls
  • Allowing a user to present their assistant's number so returned calls can be screened
  • Where a company uses a non-geographic number that is not directly carried by the Trunk provider
  • Where the company main number is on one trunk service, the company uses several trunk providers but wants to present a common number on outbound calls

The Trunks service setting template provides for the creation of custom outbound Caller ID settings. These are called "Service Numbers" and can be applied to end users:

Adding Trunk Number Ranges

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

A trunk range may be as short as a single phone number, or up to 5000 phone numbers

  • Do not add more than 300 number ranges to a trunk profile.

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, add the full numbers in E.164 format, without spaces or any special characters, for the start and end of the range. 

Trunk Number Ranges can be managed, and ranges can be added and deleted. 

Existing ranges cannot be deleted if attached to a user. 

A Trunk Number Range cannot be modified, if an adjustment is needed then it should be deleted and re-added with the revised settings.

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

Important note

With multiple trunk service profiles, ensure numbers are not duplicated or exist in more that one trunk profile as this will cause calls to fail to be routed to these numbers in the service.

Creating Service Numbers


The 'From Header' in the trunk service page must be set to Trunk Caller ID.

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 if the service provider allows them to be used for Caller ID. 

  • Presenting numbers without authorization is in contravention of the service usage terms and may be unlawful. 
  • The service provider may block numbers that are not authorized for use - so incorrectly setting the Service Number may cause 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 may reach the called party, depending on network/carrier policy. 

The Display Name is also used when managing users.

Ensure the Service Number is provided in E.164 format: 

[+][Country code][Rest of 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:


If customers want users on several different trunks to present the same Service number, then that Service Number should be defined on each trunk. The selection of Service Numbers shown in the example above are those associated with the Trunk profile. See the section below for more information.

E.164 number manipulation rules apply to Service Numbers. If the trunk profile has E.164 manipulation settings then this will modify outbound numbers in the same way as regular outbound calls.

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, select:

  • The outbound caller ID which will be their Trunk Number or DiD - this is the default setting
  • For Outbound calls to show as anonymous
  • A Service number that 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 them in order to allow the service to operate.

Where the Trunk provider may only provide one or a few numbers, an additional range should be created and applied to all users.

In this scenario a main number would typically be connected to an Auto Attendant or Call Queue.

1. Along with the short number ranges provided by the trunk provider, add a 'dummy' number range

Ensure the numbers in this dummy number range meet the following criteria:

  • They are not in the pattern of any PSTN number that may be dialled
  • They are at least 7 digits in length
  • The numbers will are formatted to comply with E.164

2. 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 their number, but this is purely for display purposes. 

As their outbound number is set by the portal, and users will be calling each other by their Teams display name, the number is not used otherwise.

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. 

Set the From Header setting to be the Trunk Caller Id (this is the default setting) to pass the modified caller Id to the Trunk provider.

Optionally set the P-Asserted-Identity Header to the Trunk User Number (this is the default setting) to 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 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 received SIP headers.  

To understand how Teams handles this, see this article: Reverse Number Lookup - Microsoft Teams


Outbound Caller ID - PBX Users

We make no provision for outbound caller ID from the portal. This is fully reliant on settings within the PBX itself - see the PBX user configuration to set this up. 


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