MIcrosoft Teams integration with PRI system.

Hi DougPCI 

We have limited devices which is certified by Microsoft for integrating with Microsoft Teams Direct Routing or PSTN Integration. The list of supported devices are as follows:-

https://docs.microsoft.com/en-us/microsoftteams/direct-routing-border-controllers

In addition in case you belong to one of the country wherein Microsoft Supports the Calling Plans you can check with your provider in case they support for Number Porting then the Numbers can be ported to Office 365 and assigned to a specific user account or Resource Account. 

Countries wherein Microsoft Calling Plans are available

https://docs.microsoft.com/en-us/microsoftteams/calling-plans-for-office-365 

With Regards,

Satish U