How to configure extension dialing in Microsoft Teams for Resource Accounts or users without PSTN numbers?

Dear @Rajasekar K,

I understand you are looking to replicate Zoom Phone's short extension dialing for users and resource accounts without dedicated PSTN numbers in Microsoft Teams.

In Microsoft Teams, there is no built-in standalone "extension mapping" table like Zoom. Teams relies heavily on the E.164 phone number format to route calls. However, achieving your goal is possible by combining Dial Plans (Normalization Rules) and assigning dummy E.164 numbers with extensions (e.g., +1234567890;ext=XXXX).

Please refer to this document: Microsoft Teams Dial plans for phone call routing - Microsoft Teams | Microsoft Learn

Since I am answering your query as a community moderator and do not have access to your specific tenant environment, I highly recommend that you raise a support ticket directly within your Microsoft 365 Admin Center (Please ask your IT administrator to perform this step).

I suggest you ask your internal backend voice administrator or Microsoft Support to investigate and implement the following approaches based on your actual environment:

Option 1: For Users without dedicated PSTN numbers

They can utilize Teams Shared Calling combined with custom Dial Plans.

• Your backend team can assign a phone number in the format of +1XXXXXXXXXX; ext=XXXX to the user.
• Then, they will create a tenant Dial Plan with a normalization rule. When an internal user dials the 3- or 4-digit extension, the rule translates it to the full E.164 number, and Teams will route it internally via Reverse Number Lookup (RNL).

Option 2: For Resource Accounts (Auto Attendants / Call Queues)

Resource accounts cannot have native extension properties applied the same way as users.

• Your backend team will need to assign a unique full E.164 number (even a non-routing "dummy" number) to the Resource Account.
• They will then configure a Dial Plan normalization rule that translates the specific 3 or 4 digits dialed by the user into that Resource Account's full E.164 number.

By opening a support ticket in your Admin Center, your backend engineers can securely review your existing Voice Routing Policies and Dial Plans to ensure these rules do not conflict with your current setup.

I hope this provides a clear path forward for your team. Please let me know if you need any further general information.

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Extension-style dialing in Microsoft Teams Phone is supported, but it works differently from Zoom Phone. There are two main patterns, depending on whether the target is a user or a resource account.

1. Extension dialing to Users (no PSTN number required)

For users, Teams supports Dial by Extension via Auto attendants:

1. Ensure each target user has an extension value in Microsoft Entra ID / Active Directory in one of these attributes:
   • TelephoneNumber / BusinessPhone
   • Mobile
   • HomePhone (legacy, not recommended)
   • OtherTelephone (legacy, not recommended)
2. Store the extension in one of the supported formats in that phone field:
   • +<phone number>;ext=<extension>
   • +<phone number>x<extension>
   • x<extension> (can be used when there is no PSTN number and only an internal extension is needed)
   Example using PowerShell:

      Update-MgUser -UserId '******@contoso.com' -MobilePhone 'x5678'
   

3. In the Auto attendant configuration, enable Dial by Extension in the call flow. When callers reach that Auto attendant, they can dial the short extension and the Auto attendant will look up the user based on the extension stored in the directory and transfer the call.

This mechanism does not require the user to have a PSTN phone number assigned; the extension can exist only in the directory attribute.

2. Extension dialing to Resource Accounts (Auto attendants / Call queues)

Resource accounts themselves are reached by:

• A direct phone number (Calling Plans, Operator Connect, or Direct Routing), or
• Being a target in an Auto attendant or Call queue menu.

Key points from the supported model:

1. Phone numbers for resource accounts
   • Resource accounts can have Calling Plan, Operator Connect, or Direct Routing numbers.
   • Direct Routing numbers with or without extensions are supported for resource accounts.
   • Assigning a Direct Routing number that includes an extension (for example +14255551212;ext=1234) must be done with PowerShell using Set-CsPhoneNumberAssignment; the Teams admin center only supports Direct Routing numbers without extensions.
2. How inbound routing works with extensions
   • For Teams resource accounts and users, the telephone number is treated as a string. If a number with an extension is assigned (for example +14255551212;ext=12345), the inbound dialed number must include the extension for Reverse Number Lookup (RNL) to match and route the call.
   • If the dialed number does not exactly match the assigned number string, the call will fail to route or follow unassigned number routing if configured.
3. Internal short extension to resource accounts
   • Teams does not provide a separate, Zoom-style “internal-only extension” field for resource accounts. To emulate short extensions, common approaches are:
     • Assign a Direct Routing number that is itself short (for example a 3–4 digit internal-only number) and route it on the SBC to Teams; or
     • Use an Auto attendant as the front door and configure menu options or Dial by Name/Extension to transfer to the resource account.

3. Role of Dial plans and voice routing

Dial plans and voice routing policies are primarily used for normalizing and routing PSTN numbers, not for creating an internal extension directory independent of numbers:

• User dial plans normalize what users dial into routable numbers (for example, converting short internal codes into full E.164 numbers) when using Direct Routing or extension dialing scenarios.
• Route-based number translation rules can normalize inbound called numbers from the SBC to match the number format assigned to users or resource accounts.
• Reverse Number Lookup for inbound calls requires the dialed number (including any ;ext= part) to match the assigned number string.

For pure internal-only extension dialing without PSTN numbers, the supported and recommended pattern is to:

• Store the extension in the user’s directory phone attribute in one of the supported formats, and
• Use an Auto attendant with Dial by Extension enabled as the entry point for callers.

For resource accounts, use phone numbers (with or without extensions) and, where internal short codes are required, implement them via Direct Routing/SBC routing or via Auto attendant menus rather than a separate Teams-only extension field.

References:

• Planning Teams dial plans for Teams Phone
• Auto attendant and Call queue dialing and voice recognition reference
• Manage Teams resource accounts
• Set up a Microsoft Teams Auto attendant
• Plan for Shared Calling
• Dialing out in Teams requires five or more digits