Calling Plan
PSTN provider: Microsoft.
SBC: none.
Numbers and porting: Microsoft provides numbers and handles ports.
Administration: Microsoft 365 and Teams admin centers.
Emergency routing: part of the service.
First-line support: Microsoft.
Business voice decisions
Microsoft Teams calling: Direct Routing, Operator Connect, Calling Plans, or a separate phone system?
Using Microsoft Teams does not by itself decide how outside calling should work. Decide whether Teams should be the phone system, how it reaches the phone network, and whether an existing carrier, PBX, or SBC stays involved, or whether a separate cloud phone system suits the requirement instead.
First decide: should Teams be your phone system?
There are two decisions here: which platform runs your business phone system, and, if that platform is Teams, how Teams reaches the public switched telephone network (PSTN) for outside calls.
Teams Phone architecture
Teams is the calling platform. People place and answer business calls in Teams, and outside calling comes from one of the PSTN options Microsoft documents. Calling users need a Teams Phone license.
Separate cloud phone system
Another provider's platform is the business phone system, with its own apps, devices, numbers, and administration, while Teams can stay in place for chat and meetings. This is not one of Microsoft's PSTN options; it is a different phone platform.
Questions that usually settle the direction:
- Will employees actually make and answer business calls in Teams, or mainly use it for chat and meetings?
- Is there an existing PBX, SBC, or carrier contract worth keeping in the design?
- Are analog devices, fax lines, or shared-space phones involved?
- Do contact-center requirements need their own platform evaluation?
- Does calling need to keep working independently of Microsoft 365?
- Who should administer calling day to day: the Microsoft 365 team, a voice team, or a provider?
Four ways Microsoft connects Teams Phone to the phone network
Microsoft's PSTN connectivity documentation currently lists four options. They differ mainly in who supplies the phone-network connection, and Microsoft allows more than one option in the same tenant.
Microsoft Calling Plan
Microsoft is the phone carrier and supplies the numbers and PSTN access. A Calling Plan is a separate license added to Teams Phone. Microsoft describes Calling Plans as its simplest PSTN connectivity option.
Operator Connect
A Microsoft-certified operator supplies the PSTN connection and numbers. You enable the operator in the Teams admin center and don't deploy your own SBC.
Direct Routing
Teams Phone connects to a carrier you choose through a Microsoft-certified session border controller (SBC), which Microsoft says is procured, installed, and managed by you, your integrator, or a Direct Routing as a Service (DRaaS) provider.
Teams Phone Mobile
A participating mobile operator's SIM number also becomes the user's Teams number. Microsoft limits it to user numbers, without auto attendant, call queue, or conferencing numbers, so it suits mobile users rather than a whole organization. Availability depends on participating operators and geography.
Who runs what: PSTN, SBC, numbers, emergency calling, and support
Most of the practical difference is responsibility. This summary follows Microsoft's documentation; each proposal should still state the split in writing.
Operator Connect
PSTN provider: the certified operator you contract with.
SBC: none for you to deploy.
Numbers and porting: the operator.
Administration: Teams admin center plus the operator.
Emergency routing: the operator.
First-line support: the operator for PSTN issues; Microsoft for Teams.
Direct Routing
PSTN provider: the carrier you contract with.
SBC: certified SBC required, run by you, an integrator, or a hosted provider.
Numbers and porting: the carrier; you assign numbers in Teams.
Administration: Teams, the SBC, and the carrier's systems.
Emergency routing: part of your design.
First-line support: the SBC vendor, escalating to Microsoft.
Teams Phone Mobile
The mobile operator supplies PSTN, numbers, and support, with no customer SBC. Emergency address handling can vary by operator.
Separate cloud phone system
Microsoft's PSTN options do not apply. The provider supplies the platform, numbers, porting, emergency calling, administration, and support on its own terms, so confirm each in its proposal.
In every case, each site's internet connection carries the calls. If call quality or outages are a concern, compare business internet or dedicated internet access for critical sites, and managed SD-WAN when several locations share the design.
When Direct Routing is worth evaluating
Microsoft's Direct Routing planning guidance describes it as a fit for organizations that:
- have an existing PSTN carrier relationship they want to keep;
- need to integrate third-party PBXs or analog devices;
- need advanced voice routing;
- want more control over their telephony infrastructure; or
- run complex or multinational voice deployments.
That control comes with ownership: the certified SBC between Teams Phone and the carrier's SIP trunks becomes part of your support model. Microsoft supports Direct Routing only with certified SBCs, certification covers specific models and firmware versions, and support starts with the SBC vendor. Running the SBC yourself, using an integrator, or buying it hosted changes who you call when something breaks; for a carrier-hosted SBC, Microsoft advises confirming the carrier can manage voice quality end to end. The SIP trunking page covers trunk capacity, codecs, and the carrier handoff.
For branches, Microsoft documents a Survivable Branch Appliance that, where the SBC vendor provides it and it is configured, lets Teams desktop clients and Teams phones at a branch keep making and receiving PSTN calls through the local SBC during an internet outage, provided the local network and SBC stay up. It has documented limits, including no location sharing on emergency calls in that mode, so confirm it with the SBC vendor rather than treating it as a promise of uninterrupted calling.
When Operator Connect or Calling Plans is worth evaluating
Neither requires your own SBC; the difference is who supplies the PSTN connection.
Operator Connect
Worth investigating when a carrier you use or want to use participates in Microsoft's Operator Connect program where you need service. Check coverage, number availability, porting support, and emergency address handling first.
Calling Plans
Worth investigating when you want Microsoft itself as the carrier. Calling Plans come in domestic, international, and pay-as-you-go types, and availability varies by country, so confirm it for every user location.
If a PBX, analog devices, or a specialized route has to stay connected, Microsoft documents combining either option with Direct Routing for those pieces.
When to evaluate a separate cloud phone system
Having Microsoft 365 does not mean Teams has to become the business phone system. A separate platform, with Teams kept for collaboration, deserves a look when:
- most calling happens outside Teams today, on desk phones, mobile apps, or a reception console, and that workflow is not expected to change;
- contact-center, queue, or reporting requirements need their own platform evaluation;
- analog or fax lines need a supported path, since Microsoft notes that faxing isn't available through Teams Phone or Calling Plan licenses;
- calling needs to be administered, or keep running, independently of Microsoft 365;
- a voice team or provider, rather than the Microsoft 365 administrators, should own the phone system.
None of those makes a separate platform the default. SourceNet compares cloud phone systems as well as Teams calling paths, so both can be scoped against the same requirements.
Numbers, porting, and running old and new side by side
Existing numbers may be portable, depending on the number type and the providers involved. Who handles the port depends on the architecture: Microsoft for Calling Plans, the operator for Operator Connect, and your carrier for Direct Routing.
Inventory every number before choosing an architecture: direct dials, main and toll-free numbers, auto attendant and queue numbers, and any fax, alarm, or analog lines. Microsoft's porting guidance lists numbers that can't be transferred, including numbers dedicated to faxing and numbers used for data connections. Numbers that don't fit the chosen architecture need their own plan.
Keep the existing service active until every port is confirmed and tested. Inactive or disconnected numbers can't be ported, and the FCC's porting guidance warns against canceling service before the port is complete. If an existing PBX stays in place during migration, a hybrid design with Direct Routing can keep it connected; that overlap needs its own routing, numbering, and support plan. Moving numbers between Teams options later is another port with its own steps.
Emergency calling across sites and remote users
Each option splits the emergency-calling work differently. Calling Plan and Operator Connect users are enabled for emergency calling automatically, and in the United States and Canada those providers supply dynamic emergency routing. With Direct Routing, your design defines emergency call routing policies and connects either an emergency routing service provider or an ELIN application on the SBC.
Location is the harder part: Microsoft's dynamic emergency calling depends on administrators linking subnets, Wi-Fi access points, and switches or ports to validated emergency addresses at every site. Remote users depend on location sharing from their devices, and Microsoft notes that the Teams web client doesn't support dynamic emergency calling.
U.S. multi-line telephone systems are also subject to federal requirements under Kari's Law and RAY BAUM'S Act, which the FCC's MLTS 911 guidance summarizes. This isn't legal advice. Confirm with each provider how emergency calls will behave for every site and type of user, and test before cutover.
What to compare in Teams calling proposals
Give every provider the same users, sites, numbers, and devices, then check each proposal against these points before comparing totals.
Licensing assumptions
Which users need Teams Phone, which need a Calling Plan or operator service, and what the proposal assumes you already own.
PSTN and SBC
Who supplies PSTN connectivity, whether an SBC is involved, the certified model and firmware, and who hosts, monitors, and updates it.
Numbers and porting
The full number inventory, which numbers move, who files each port, and how numbers that can't move are handled.
Emergency calling
How locations are defined for each site and for remote users, who keeps them current, and how the design will be tested.
Sites, countries, and outages
Service availability for every location and user country, and what happens to calling at a branch that loses internet.
Coexistence and support
PBX, analog, and carrier dependencies during migration, who performs each implementation task, and who takes the first support call at each boundary.
SourceNet can help scope those assumptions and compare the workable paths. SourceNet is not Microsoft or a carrier; the provider you choose supplies the service.
Technical references
The Microsoft and FCC documentation behind this page. Microsoft updates its Teams Phone guidance regularly.
Microsoft docs
PSTN connectivity options
Microsoft's overview of the four Teams Phone PSTN options.
Read the overview →Microsoft docs
Plan Direct Routing
Requirements and support boundaries for Direct Routing.
Read the planning guide →Microsoft docs
Certified SBCs for Direct Routing
The SBC models and firmware Microsoft supports.
See certified SBCs →Microsoft docs
Plan for Operator Connect
What the operator and Microsoft each manage.
Read the Operator Connect guide →Microsoft docs
Microsoft Teams Calling Plans
Plan types and availability when Microsoft is the carrier.
Read about Calling Plans →Microsoft docs
Porting numbers to Teams
Which numbers can move and what a port order needs.
Read the porting guide →Microsoft docs
Plan and manage emergency calling
Emergency addresses and routing by PSTN option.
Read the emergency calling guide →FCC guidance
MLTS 911 requirements
Federal 911 rules for multi-line phone systems.
Read the FCC guidance →FCC guidance
Number portability guidance
Why you shouldn't cancel old service before porting.
Read the FCC guidance →Microsoft Teams calling FAQ
What is the difference between Direct Routing and Operator Connect?
With Direct Routing, a Microsoft-certified SBC run by you, an integrator, or a hosted provider connects Teams Phone to a carrier you choose. With Operator Connect, a Microsoft-certified operator supplies the PSTN connection and numbers, and you don't deploy your own SBC.
Does Microsoft Teams Direct Routing require an SBC?
Yes. Microsoft supports Direct Routing only with a Microsoft-certified SBC, which you can run yourself or obtain through an integrator or hosted provider.
Can we keep our existing carrier with Teams Phone?
Through Direct Routing, a carrier you already use can supply PSTN connectivity behind a certified SBC. Through Operator Connect, only if that carrier participates in Microsoft's program where you need service.
Can we keep our existing phone numbers?
Existing numbers may be portable, depending on the number type and the providers involved. Confirm portability for each number before committing to a migration.
Can Teams run alongside our existing PBX during migration?
It can, depending on the design. Microsoft documents hybrid deployments that use Direct Routing to connect Teams with third-party PBXs and analog devices.
Do we need Teams Phone licenses?
Yes, for calling users under every option. Calling Plans add a separate Microsoft license; the other options add an operator or carrier contract, and Direct Routing also needs an SBC.
Is Operator Connect available everywhere?
No. It depends on which operators participate and the countries or regions each one serves, as listed in Microsoft's Operator Connect directory.
Should we use Teams Phone or a separate cloud phone system?
It depends on where people will actually make calls, existing PBX and device needs, contact-center requirements, and who should run calling. Compare both against the same requirements.
Related voice and network decisions
Compare the Teams calling paths that fit your setup.
Bring your Microsoft 365 licensing, current PBX or SBC, number inventory, sites, and current calling setup. SourceNet can help compare the workable calling paths; you choose the provider.