Simple Understanding on ways to enable Microsoft Teams PSTN Calling Services
Updated: Mar 13, 2022
From the first release of Microsoft Teams to present times, Microsoft came up with various options to enable PSTN telephony with MS Teams. Customers many time face challenges in choosing among various options available basis on their site specific needs and challenges.
Here I’ve tried to include all major approaches through which PSTN calling services can be enabled in MS Teams and decision points on which your choice can be based upon.
MS Teams Calling Plans
This is the most simple and straightforward way to enable your users for PSTN calling in MS Teams, where you buy either Domestic or International Calling Plan Licenses directly from Microsoft and assign it to users. These license comes with Calling minutes which is pooled for all users belonging to same region/country. For example - if you have 10 users in same country with a 120 minutes Domestic Calling Plan assigned, they share a pool of 1,200 minutes. All calls exceeding these minutes are billed per minute.
For more details, please refer to Microsoft official pages. Below diagram is the simple representation of high level Calling Plan architecture.
Is Calling Plan a viable option for you? You can choose Calling Plans method to enable MS Teams PSTN services basis on (but not limited to) these decision points -
Availability of Calling Plans in your region/country. To check for availability, refer to Calling Plan Availability in your Country/Region.
You have relatively simple needs with no dependencies on any legacy on premises telephony systems. Example - you do not want third party on-premises PBX or other telephony integrations.
If you have existing on-premises deployments for telephony, you want to move away from it and transform completely to Cloud telephony.
You want Microsoft to manage all your Calling related services, with no dependency on Local telecom providers.
You want to minimise your operational & maintenance cost.
You do not want to invest on any hardwares like Session Border Controllers.
You want faster and easier deployment.
MS Teams Operator Connect
Operator Connect is another way to enable your users for MS Teams PSTN Telephony services. In this deployment model, your preferred telecom provider manages the PSTN calling services, and you can manage them directly from Teams Admin Center.
Below is simple representation of Operator Connect high level architecture.
Is Operator Connect a viable option for you? From customer’s perspective, Operator Connect is also a Cloud deployment model, alongside Calling Plans, so many decision points for Calling Plans are also applicable for Operator Connect. Let’s understand them here again -
The Calling Plans are not available in your country/region.
Your new & preferred telecom carrier is a participant in the Microsoft Operator Connect program. Please refer to this page to check if your carrier is part of the program.
You have relatively simple needs with no dependencies on any legacy on premises telephony systems. Example - you do not want third party on-premises PBX or other telephony integrations.
If you have existing contracts with telecom carriers for your current legacy telephony setup and want to reutilise it, you can do so after making sure that your carrier is part of Operator Connect Program.
You want to minimise your operational & maintenance cost.
You do not want to invest on any hardwares like Session Border Controllers and want them to be managed by carrier.
You want faster and easier deployment.
MS Teams Direct Routing with Customer Managed Session Border Controllers
Using this deployment model, you will get more flexibility & control in terms of configuration of different calling scenarios, manipulating calling or called identities such as adding or removing prefixes, integrations with other PBX systems, analog devices etc. In this model, you deploy a customer managed Session Border Controller which connects with Microsoft Teams Phone System on one side, and your local telecom carrier on the other. Both options of placing SBC physically or virtually (in customer managed Cloud or VM) are available from major certified SBC Vendors.
Below is the simple representation of this deployment model.
Where do you choose this deployment model? Let’s understand the decision points basis on which you may opt for this model -
You have complex UC infrastructure, where you have a requirement of integrating other systems as well like third party private branch exchange (PBX) systems, a Contact Center application, Analog gateways, DECT phones etc.
You want to retain your incumbent telecom carrier contracts which are currently providing services to your existing telephony system.
You have complex dialling routing patterns where manipulation in called or calling identities are frequently required.
You have existing investments on Session Border Controllers that might be in use to support your legacy telephony system. Example - Skype for Business Enterprise Voice, Cisco Call Manager. Please refer to this page to view the list of all certified vendors and models of Session Border Controllers (SBCs).
The trunk connectivity from telecom carrier is physical in nature like (E1, T1 or analog lines). In this case, you need to deploy the physical SBC. With virtual SBCs, only SIP trunks are possible.
MS Teams Direct Routing with Carrier Managed Session Border Controllers (Direct Routing as a Service)
This model is similar to the above one, except the fact that SBCs are also managed by carriers and not customer. Currently, all major telecom carriers are providing this model in most countries. For details on availability you need to get in touch with carriers individually.
Below is the simple representation of this deployment model.
