MIcrosoft Teams integration with PRI system.

DougPCI 

Hi Doug - hope you and family are safe.

To add to Satish's note, here's a summary of PBX integration options:

1. The model to integrate your existing PBX with Teams would be via Direct Routing.  This can be done via on on-prem SBC, hosted virtual SBC &/or a "direct routing as a service" provider.

2.  In ROI terms, you're comparing cost of ongoing support of existing PBX + cost of current PSTN usage model + cost of SBC vs. cost of MSFT's call plans (in US, this is $12/user or other options if Enterprise Agreement).  You can also do a mix.  If you decide to use any MSFT calling services, you can port your numbers to MSFT (as per the country list Satish listed).

3.  In licensing terms, both models require a pre-req license with Teams (like E1, E3, E5, etc), Phone System license & Audio conferencing service is currently tied to MSFT service (vs use of Direct Routing).

4.  Re:  conferencing - you can port your number(s) to use as Teams bridge lines.  Teams conferencing is PSTN, VOIP, Video, Web up to 250 users.  Or - up to 10,000 with the "Live Event" (webinar) service.

5.  Re:  PBX options --- Teams as Auto Attendant, Call Queues, CDR Logs & a other related toolsets to manage the service.

Hope this helps.

David Bleecker