To make and receive ordinary phone calls in Microsoft Teams, each user needs a Teams Phone licence plus a connection to the public phone network. Microsoft offers three ways to connect: Calling Plans, where Microsoft is the carrier; Operator Connect, where a participating carrier plugs its service into Teams; and Direct Routing, where you connect SIP trunks from a carrier of your choice through a certified session border controller. Calling Plans are the simplest, Operator Connect adds carrier choice with little setup, and Direct Routing gives the most control and flexibility.
If your staff already spend the day in Teams, making it the phone system is a natural step. The licensing and connection choices are where most of the confusion lives, so here they are in order.
What Teams Phone is
Teams Phone is Microsoft's calling feature for Teams: extensions, call transfer, voicemail, auto attendants and call queues, all inside the Teams app and on certified desk phones. Some enterprise Microsoft 365 suites include it, and for others it is an add-on licence per user. Microsoft revises its licence names and bundles from time to time, so confirm the current terms for your agreement.
Teams Phone on its own lets users call each other inside your organisation. To reach outside numbers, and to be reachable on a normal phone number, you need one of the three connection options.
The three options side by side
| Calling Plans | Operator Connect | Direct Routing | |
|---|---|---|---|
| Who is the carrier | Microsoft | A participating carrier you choose | Any SIP trunk provider you choose |
| Session border controller | None needed | Run by the carrier | Yours, or hosted by a provider |
| Where numbers are managed | Teams admin centre | Teams admin centre | Configured through your SBC and Teams settings |
| Setup effort | Low | Low to moderate | Higher |
| Availability | Limited to the countries Microsoft serves | Wherever participating carriers operate | Wherever you can get SIP trunks |
| Legacy PBX, analog devices, paging | Not directly | Limited | Yes, through the SBC |
| Good fit | Small offices wanting minimal setup | Organisations wanting carrier choice without running an SBC | Larger or complex estates, or anyone with special requirements |
Microsoft also offers Teams Phone Mobile in some markets, which ties a mobile number to Teams through a participating mobile carrier. It is a separate decision and not covered here.
How Direct Routing works
With Direct Routing, a session border controller (SBC) sits between Microsoft's cloud and your SIP trunk provider. The SBC must be a model Microsoft has certified for Direct Routing.
- Teams side. The SBC connects to Microsoft's phone system over SIP secured with TLS, with call audio encrypted using SRTP. It needs a public DNS name and a publicly trusted certificate.
- Carrier side. The SBC connects to your SIP trunks, the same kind of trunks described in SIP trunking vs hosted PBX.
- Routing. In Teams, voice routing policies and PSTN usages decide which calls go to which SBC and trunk. Dial plans normalise how users enter numbers.
Own the SBC or have it hosted
You can run the SBC yourself, on hardware or as a virtual machine, or use a provider that hosts SBCs and connects them to its own trunks. Hosted takes most of the configuration off your plate. Owning it gives full control, and it is how you connect an existing PBX, analog gateways for fax and paging, or a contact centre platform during a migration.
Where Direct Routing earns its complexity
- A phased migration. The SBC can route calls between Teams users and an existing PBX, so you move departments one at a time instead of all at once.
- Analog and special devices. Fax lines, overhead paging, door entry and lobby phones can stay connected through gateways behind the SBC.
- Carrier choice. You can buy trunks from whoever prices your call volumes best, and change later without changing the phone system.
- Resilience. Multiple SBCs in different locations, and trunks from more than one carrier, can remove single points of failure.
- Locations Microsoft does not serve. If you have offices where Calling Plans are not available, Direct Routing can fill the gap.
What all three options still need
- A good network. Teams calls are sensitive to jitter and packet loss. Each office needs a solid circuit such as dedicated internet, local internet breakout rather than routing everything through head office, and traffic priority for Teams media on your network. For multiple sites, SD-WAN helps keep calls on the best path.
- Emergency calling configured. Teams supports emergency addresses and dynamic emergency calling based on network location. Set it up properly; the rules are in E911 rules for business phones.
- Resource accounts for auto attendants and call queues, each with the appropriate licence.
- Shared-device licensing for lobby, conference room and warehouse phones.
- Number porting from your current carrier to whichever option you choose. See porting business phone numbers.
A worked example
A hypothetical company with invented user counts and call volumes, used to show the decision. No prices are implied.
Suppose a company has 150 staff across offices in New York and Miami, all already using Teams for chat and meetings. It has an old PBX whose maintenance contract ends in six months, 12 lobby and conference phones, 6 analog devices (two fax lines, overhead paging and three door-entry units), and a peak of about 25 simultaneous outside calls.
Calling Plans would be simple for the 150 users, but would not connect the paging, door entry or fax, and would force a single cutover date for everyone.
Operator Connect would give carrier choice with little setup. It might handle most users well, with the analog devices needing a separate solution.
Direct Routing with a hosted SBC would let the company connect the PBX during the transition, keep the analog devices on gateways, and buy 30 SIP paths (25 at peak plus headroom) from the carrier that prices them best. It could move Miami first, then New York department by department, porting numbers in batches as each group moves.
For this company, Direct Routing fits because of the analog devices and the phased move. A 20-person office with nothing but laptops and mobiles would likely be better served by Calling Plans or Operator Connect.
Where Direct Routing projects go wrong
- Certificates that expire. The SBC's public certificate has to be renewed on time. When it lapses, calls stop, usually on a day nobody expects.
- Number formats. Teams expects numbers in full international format. If the SBC and the carrier disagree on how a number is written, calls fail or caller ID shows the wrong thing. Test inbound, outbound and transfers.
- Firewall rules. The SBC must reach Microsoft's signalling and media addresses, and Microsoft publishes the ranges and ports. A firewall change months later can break calls in one direction only, which is confusing to diagnose.
- One SBC, one site. A single SBC in a single office is a single point of failure for the whole company's calling. Hosted SBCs in more than one data centre, or a second SBC of your own, remove it.
- Nobody owns it. Direct Routing sits between the Microsoft team, the network team and the carrier. Decide in advance who takes the call when something breaks.
Media bypass and call quality
By default, call audio in Direct Routing can travel through Microsoft's network on its way between the user and the SBC. With media bypass enabled, audio can flow directly between a user's Teams client and the SBC when they are on the same network, which can shorten the path for office users. It needs more careful network and firewall planning, so it is worth discussing with whoever configures the SBC, especially for offices with heavy call volume near the SBC.
A sensible rollout order
- Assess the network at each site for Teams call quality before moving anyone.
- Confirm licences for users, shared devices and resource accounts.
- Set up emergency addresses and network locations.
- Connect the chosen option and test with a pilot group on temporary numbers.
- Port numbers in batches, one group or site at a time.
- Retire the old PBX and any leftover lines once everything is confirmed working.
Questions to ask your provider
- Do you offer Operator Connect, Direct Routing, or both?
- For Direct Routing, do you host the SBC, and is it on Microsoft's certified list?
- How are SIP paths and calls priced for my volumes?
- How do you handle emergency calling and location for Teams users, including remote workers?
- Can you connect my existing PBX and analog devices during migration?
- What happens to calls if one SBC or data centre fails?
- Who manages number porting, and can it be done in batches?
Getting Teams calling priced
We compare Operator Connect and Direct Routing providers side by side, together with the circuits at each office, and we will tell you if Calling Plans are all you need. The provider pays us, so there is no markup, and you deal with one agent from quote to cutover. See our voice and UCaaS page for more. The quote is free with no obligation and you usually hear back the same day. Tell us your user count and sites, call 478-758-8091 or text (347) 870-0965.
