Does MS Teams Extension SDK provide any kind of API that can be used for custom caller identification?
Their documentation only mentions Azure AD and local contacts:
Phone System shows the incoming external phone number as the caller ID. If the number is associated with a user or contact in Azure AD or a personal contact, the Skype for Business and Teams clients will show the caller ID based on that information. If the phone number is not in Azure AD or a personal contact, the telco-provided display name will be shown if it is available.
Is it possible for an extension, or a bot, to provide additional sources for lookup? For example, iOS has Call Directory App Extensions which allow resolving a caller's number against some external source in a secure way - does Teams have (or plans to have) anything similar?
Unfortunately this turned out to be impossible. Confirmed by a Microsoft Tech Support employee in private communication.