Does GCC High Teams calling work if some of our employees are still on a commercial Microsoft 365 license?

GCC High Teams calling works for users licensed in the GCC High tenant, but it does not extend to employees on a commercial Microsoft 365 license. The two tenants operate as separate, isolated environments with no native interoperability for Teams calling or file sharing.

Many organizations use an "enclave" approach where only employees who process, store, or access CUI are licensed in GCC High, while the rest of the workforce stays on commercial Microsoft 365. This reduces licensing costs because GCC High licenses are priced higher than commercial equivalents. The trade-off is operational complexity: users in the commercial tenant cannot directly call GCC High users through Teams-native calling. They can reach each other through standard PSTN phone numbers (dialing the actual phone number), and cross-cloud B2B guest access can be configured through Microsoft Entra for limited meeting and collaboration scenarios. Organizations running a split-tenant model need clear data governance policies that define which employees handle CUI, which workflows stay within GCC High, and how cross-tenant communication is managed without creating compliance gaps.