Note: Phone App is available as an additional 'add-on' to existing PBX or Trunk services. If the options is not available in the portal then the service has not been provisioned to the account and needs to be enabled via the licensing provider. 

Phone App is currently only available to Call2Teams for PBX users. (Call2Teams for Trunks coming soon!) 

Applies To

Call2Teams -Customer 


Calls not going through to a Teams user - '603 Call Declined' in the call log

This issue is a result of the customer's Microsoft 365 account not being correctly set for External Access and allowing the Phone App domain.

The solution is to allow the Phone App domain on the Microsoft 365 tenant in the external access settings or allow all domains

Note: it can take some time (maybe several hours) for the External Access domain settings to take effect in the Teams admin centre


Phone App relies upon the service global network to place calls directly to Microsoft Teams users through a method referred to as ‘external access’.  External access is managed within the Teams admin center, and a function of this management is to enable calls from the domain used by the service for Phone App ( ).

Microsoft tenants have this capability fully enabled by default but if external access has been restricted then this is managed in the Teams admin center:  

Using the Microsoft Teams admin center

  1. In the left navigation, go to Users > External access.

  2. Turn on the Users can communicate with other Skype for Business and Teams users setting to enable External Access.

    Screenshot of Users can communicate with other Skype for Business and Teams users setting turned on
  3. If all Teams external organizations are to communicate with the organization, skip the next step; the Microsoft tenant is ready for external access.

  4. If a limit to the organizations that can communicate with users in the organization is needed,  either allow all except some domains, or allow only specific domain

    • To limit communications to specific organizations, add those domains to the list with a status of Allowed. Once these are added any domain to the Allow list, communications with other organizations will be limited to only those organizations whose domains are in the Allow list.
    • Be sure to add the Phone App domain ( ) to the Allow list.
    • Click Save.


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