Can a subcontractor use GCC High Teams calling to receive calls from a prime contractor on a standard commercial tenant?

GCC High and commercial Microsoft 365 tenants are isolated environments, so standard Teams-to-Teams calling between them does not work natively. A subcontractor on GCC High cannot receive a direct Teams Phone call from a prime contractor on a commercial tenant as if they were on the same platform.

Cross-cloud communication is possible through specific configurations. Microsoft Entra business-to-business (B2B) collaboration can be set up to allow limited cross-cloud guest access, and Teams Cross-Cloud Guest Access enables commercial tenant users to join GCC High Teams meetings with some limitations. However, for regular PSTN voice calls (standard phone calls using phone numbers), the call simply routes through the public telephone network regardless of which Microsoft cloud environment either party uses. The subcontractor's GCC High Teams Phone number rings like any other phone number when dialed from any phone, including a commercial Teams tenant. The compliance boundary is maintained because the subcontractor's call data, metadata, and logs stay within the GCC High environment. The limitation applies specifically to Teams-native calling features and collaboration, not to traditional phone calls between numbers.