Those organizations who want to fully move to Microsoft Teams, but are dependent on 3rd party voice add on apps have been asking us regularly when PSTN Numbers can be assigned to Microsoft Teams Bots.
According VinodRavichandran, the answer is: "PSTN Calling is planned for this year, potentially Q3."
This should allow PSTN callers to dial into voice apps built using the Teams Calling API like IVR's and other custom voice apps.
Source:
https://github.com/microsoftgraph/microsoft-graph-comms-samples/issues/29#issuecomment-465684066
