Cloud Voice - Microsoft Teams
Operator Connect. If your existing carrier participates in the Microsoft Operator Connect program, they can manage PSTN calling and Session Border Controllers (SBCs)
Direct Routing. This enables you to use your own PSTN carrier by connecting your Session Border Controller(s) (SBC) to Phone System
Calling Plans are quick and easy but don't represent great value as you scale, and the calling tariffs aren't great
Operator Connect is fine as long as you're able to accept the limits imposed by the carrier. There was after all a reason that PBXs became popular
Direct Routing offers the most flexibility but is the most complex, this allows you to maintain your existing arrangements, including your PBX
Others options are available such as plugin applications, bots, etc but these can break the Teams experience
ACME UC offer calling plans via CSP, Direct Routing solutions and options as well as fixed all in, per month contracts suitable for smaller businesses.