Choosing a PSTN connectivity solution
There are a few configurations available for your PSTN connectivity solution. PSTN allows your users to make calls outside your company to any number in the world.
The easiest telephony solution to implement with Microsoft Teams is Microsoft 365 Business Voice. This is a cloud-based solution in which Microsoft is your PSTN carrier and provides Private Branch Exchange (PBX) capabilities so your users can make calls within the organization as well as globally. Microsoft 365 Business Voice is available as a separate add-on subscription but limited to 300 users or is included in Microsoft 365 E5 subscriptions (300 or more users).
As for your complete solution, all organizations will require Phone System (included in Business Voice). For connectivity to PSTN for global calling, you can choose Microsoft for the carrier or connect your existing carrier with Direct Routing.
Microsoft supports different configurations that might work better for...