With Microsoft Teams Phone, we have been steadfast in our belief that the future of calling is built on Voice over Internet Protocol (VoIP) calling that delivers rich voice and video experiences across organizational boundaries.1 Additionally, Teams Phone VoIP calling capabilities are complemented by an enterprise-grade public switched telephone network (PSTN) service that provides customers with the ultimate flexibility in how they communicate and collaborate.

In June 2022, Microsoft reached the milestone of 12 million Teams Phone PSTN users. Doubling the number in a year!! Microsoft is competing with the local telcos. Hard to imagine Microsoft as telco.
The stiff competition is really heating up.

Stay connected with Microsoft Teams Phone | Microsoft 365 Blog