Set up cross-company calling for Dynamics 365 Remote Assist (for admins)
Users in your organization can make or receive a one-on-one call with a Microsoft Teams user from another company (domain) if external access is enabled in Microsoft Teams for each domain.
At this time, group calling and file sharing is not available for cross-company calling.
Enable external access in your Microsoft Teams admin center. This allows users in your organization to make calls and chat with users outside your domain.
By default, users can communicate with users in any other domain that has external access turned on and that has allowed external access with your domain. If you want to restrict this behavior, you can add allowed or blocked domains. For more information, see Manage external access (federation) in Microsoft Teams.
To check to see if a contact in another domain has external access enabled in their company’s Microsoft Teams admin center, try typing the contact's full email address in Teams Desktop. When external access is allowed between both domains, Teams shows the following message: