Which voice providers can add PSTN calling to a Microsoft 365 GCC High tenant for a DoD contractor?

Only Direct Routing as a Service (DRaaS) providers with GCC High-certified infrastructure can add PSTN calling to a GCC High tenant for a DoD contractor. The provider must operate Microsoft-certified SBCs connected to Azure Government, maintain U.S.-only data pathways, and meet DFARS, ITAR, and CMMC compliance requirements for their own operations.

Providers identified in the market include Atlantech Online, CallTower, HelloTeams, Momentum, AT&T, and Aura. Some managed service providers like Summit 7 and Spyderweb Communications also offer GCC High voice solutions, often through partnerships with carrier-level providers. The selection pool is intentionally small because the compliance, infrastructure, and personnel screening requirements create a high barrier to entry. Organizations should confirm that any provider under consideration has explicit GCC High SBC certification (not just commercial Teams Direct Routing experience), operates compliant infrastructure for call routing and metadata storage, and can demonstrate alignment with the specific frameworks referenced in the organization's DoD contract.