With over 320 million monthly active users (Microsoft, 2024), MS Teams has dominated the collaboration market, offering a compelling blend of chat, file sharing, video conferencing, and third-party integrations. As organisations continue their digital transformation journeys, Teams has evolved into a fully-fledged business phone system with Microsoft Teams Phone.
To integrate external calling capabilities within Teams, adding Public Switched Telephone Network (PSTN) connectivity is essential. This enables users to make and receive calls to and from traditional phone numbers directly from the Teams interface. However, there is no single approach to enabling PSTN connectivity in Microsoft Teams, and organisations must evaluate different solutions based on cost, flexibility, scalability, and control.
There are now over 20m Teams Phone PSTN users globally.
Bringing Voice into Microsoft Teams: What’s Required?
Before diving into the available PSTN connectivity options, it’s important to understand the fundamental components required to enable voice calling in Teams:
- Microsoft Teams Phone License: Businesses need to purchase a Microsoft Teams Phone license to unlock calling features.
- PSTN Connectivity: This can be achieved through Microsoft’s Calling Plans, Operator Connect, Direct Routing, or Teams Mobile.
- SIP Trunking or Carrier Services: Businesses that opt for Direct Routing will require a SIP trunking provider and a certified Session Border Controller (SBC).
Exploring the PSTN Connectivity Options
Organisations can choose from four main methods to connect Microsoft Teams to the PSTN:
Let’s take a closer look at each option.
1. Microsoft Calling Plans
Microsoft Calling Plans is an all-in-the-cloud solution where Microsoft acts as the PSTN carrier/telephony provider. You set up and manage phone numbers directly through Microsoft Teams with Microsoft managing the infrastructure.
Advantages of Microsoft Calling Plans
The main benefit of Calling Plans is that it can be easy to deploy and all with the Microsoft Environment so no need for additional infrastructure. It’s perfect for small businesses, maybe 10-30 people, with limited IT capabilities, especially if keeping existing phone numbers is not important.
Disadvantages of Microsoft Calling Plans
The downside of the ‘out of the box’ solution is that it can get expensive as you scale, and you are also charged for inbound calls. If you want to keep your existing numbers, you need to be aware than the transfer of DDIs (Direct Dialing In numbers) can take months. One thing that is not well known is that your existing numbers transfer to Microsoft ownership. So, if you decide to move provider in the future, Microsoft are not legally obliged to release your numbers.
Finally, as things stand there is limited regional availability and calling plans are only available in selected countries. That is improving all the time but should be noted for multi-country businesses.
2. Operator Connect
Operator Connect (OC) allows businesses to bring their preferred telecom provider into Microsoft Teams through Microsoft’s curated list of approved operators. OC is kept fully within the MS Environment and manged by the operator.
Advantages of Operator Connect
OC has similar benefits to Calling Plans, like simple configuration and user management and no additional hardware. But it goes further by allowing organisations to keep the existing calling provider, and the DDIs, without the need to manage the telephony environment themselves. Also, this is an option often promoted by Microsoft’s own sellers as the fastest way to enable Teams Voice.
Sounds great! So why don’t all businesses choose OC?
Disadvantages of Operator Connect
- Limited set of Microsoft-approved operators: OC is bound to a limited set of Microsoft-approved operators, reducing the control an enterprise has over its infrastructure i.e. for service quality and availability. This is relatively new technology for the operators and the feedback from the market is that many are not equipped to provide the ongoing porting and support needs for customers, especially for more complex organisations.
- Missing integration options: The downside of being fully-cloud is that it doesn’t allow for hybrid or integration options for fax, analog, alarm servers, on-premise tools etc that some verticals, regulations must have. This is something that the MS sellers often forget when advising customers as the cloud is their focus.
- Hidden dependencies: While they are not quite ‘hidden costs’, prospective buyers need to understand where their existing carrier contract obligations remain as well as the management and maintenance of on-premise hardware and third-party systems.
At Damovo we have happily recommended and helped implement OC to customers as a fast, cost-effective option. However, we have had far more instances where the total cost of migration via OC outweighs the benefits to the business, so need another option.
Best suited for:
- Mid-sized to large enterprises with existing carrier relationships.
- Businesses seeking a balance between control and ease of deployment.
- Cloud-only strategy with speed to transform a priority over budget.
Not ideal for:
- Companies requiring full autonomy over telephony architecture.
- Businesses with existing carrier contracts especially multi-country/carrier.
- Complex organisations with hybrid requirements
3. Direct Routing
Direct Routing (DR) allows businesses to connect Microsoft Teams to any PSTN provider via a certified Session Border Controller (SBC), enabling maximum flexibility. This allows MS Teams to function as a complete business phone system, integrating with your current telephony setup.
The SBC can either be on-premise or in the cloud, providing intelligent routing and management of voice traffic. The SBC is the ‘secret sauce’ in Direct Routing,
- serving as the gateway between Teams and the PSTN provider,
- allowing custom call routing, and
- cost-efficient traffic as well as
- acting as a translator between different telephony providers.
For these reasons, this is the preferred method for Enterprises who want to keep their legacy UC infrastructure for parts of their business, while allowing Teams collaboration and voice for other areas.
Advantages of Direct Routing
Flexibility is the key word when considering Direct Routing. It allows total control over the choice of carrier, call routing, and telephony costs.
- Allows integration with legacy on-premise PBX systems.
- Business can use existing DDIs and retains ownership
- Can be more cost-effective for enterprises with high call volumes.
- Enables advanced call handling, compliance, and redundancy options.
Disadvantages of Direct Routing
Sounds great! But what do organisations need to consider with Direct Routing?
- Technical know-how: Firstly, it requires technical expertise for deployment and management so best practice is to use a partner to design, implement and often support.
- Additional costs: There are additional infrastructure needs such as SBCs, so some upfront costs not associated with Operator Connect or Calling plans.
- Longer implementation: Finally, there are usually longer implementation time compared to Calling Plans and Operator Connect although automation improvements are reducing this gap.
Best suited for:
- Medium to Large enterprises requiring custom telephony configurations.
- Best choice for complex telephony, multi-vendor environments
- Businesses with existing SIP trunking agreements.
- Organisations operating in multiple regions
Not ideal for:
- SMBs with limited IT resources.
- Companies prioritising a quick and easy deployment over cost
4. Teams Mobile (Future Option)
An interesting consideration for the future: Microsoft is exploring the potential of integrating Teams Mobile as a standalone PSTN connectivity option, leveraging mobile carriers for native calling, integrating mobile carriers to provide a single number across both Teams and native mobile diallers.
It is available today but very much in its infancy. We’ve seen estimates that less than 5% of Microsoft PSTN Customers are using Teams Mobile, but there are no official figures available to date.
Why might Teams Mobile be of value for some businesses?
It could provide fully mobile-first experience with integrated Teams calling. So seamless transition between cellular and Teams environment and eliminating the need for additional infrastructure or SIP trunking.
So far there is limited initial carrier support and businesses would need a mobile-centric strategy rather than a fixed telephony approach to consider it at this stage.
There are also some connectivity and quality of service concerns that need to be improved upon before it will be widely adopted.
If we look at some recent partnership announcements by Microsoft: AT&T, Virgin Media, O2, and Vodafone UK, the solution will grow. It’s also good to look at the competition and Cisco is also investing heavily in its mobile equivalent, Webex Go, extending its Webex calling capabilities directly to a user’s phone
So very much a watch this space!
The Future of Voice in Microsoft Teams
As hybrid work continues to redefine business communications, Microsoft Teams is positioned as a central hub for collaboration and voice services. The demand for cloud-based telephony solutions will only increase, driving more innovation in PSTN connectivity.
- AI-powered call analytics and automation will enhance Teams calling experiences.
- 5G and edge computing will improve real-time communication quality and reliability.
- Deeper integration with contact centres will make Teams an all-in-one customer engagement platform.
- Greater regulatory compliance capabilities will slowly expand Teams’ presence in heavily regulated industries such as healthcare and finance.
With Microsoft continually enhancing its Teams Phone capabilities and providers expanding their offerings, decision makers must stay informed on the latest connectivity options to ensure they choose the best PSTN solution for their business needs.
Are you considering bringing voice capabilities into Microsoft Teams?
Schedule a call with us to discuss what option is best for your business now and in the future.
