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Teams Calling FAQs

Sometimes on our webinars, we don't have time to answer all the great questions we receive. We've captured some here about Teams Phone System. The topics cover Calling Plans and Direct Routing, Session Border Controllers (SBCs), e911 routing, porting numbers, and survivability.

If your questions aren’t answered here, please send an email to or reference one of the links within this FAQ.t factors favor

What factors favor Calling Plans versus Direct Routing?

  1. Cost – generally, large/centralized organizations opt for Direct Routing. There are exceptions, but we generally see the tipping point favor direct routing for orgs over 300 users.
  2. Administrative overhead – while Direct Routing may have a lower operational cost than calling plans, it will require management/patching/monitoring of the Session Border Controller, adding to the TCO. Organizations without a telcom/IT staff are best suited for Calling Plans.
  3. Integration and survivability requirements – local SIP trunks, analog integrations, and co-existence with phone systems are only supported with Direct Routing.

See more decision analysis at Deciding Between Direct Routing and Calling Plans (

How often do SBCs tend to need software updates and config changes?

AudioCodes puts out SBC Updates irregularly. They seem to always have a Long Term Support (LTS) and a Latest Release version. AC recommends that customers use the LTS version unless they need a new feature in the LR version. Looking at the 7.2 LTS's, they have come out on:

8/3/20, 10/25/20, 11/5/20, 12/17/20, 12/28/20, 1/11/21 - So quite irregularly - 15 in 2020 and 13 in 2019.

Once an SBC is configured you will rarely change the configuration. If you use TLS for management or authentication and encryption, you will every few years have to update your certificate and update the Root Chains as required. If you are using Dial Plans and doing a migration, you will be touching the SBCs to update the Dial Plans each time you do a migration.

Can there be a hybrid setup with some users on Calling Plans and others on Direct Routing?

Yes, Direct Routing is a common set up for numbers or users that rely on analog or legacy solutions that are not supported in Teams (Call Center Software). Calling Plans are ideal for mobile information workers.

Is a on prem SBC the same as a PBX?

No, the SBC (Session Border Controller) is a VoIP gateway & voice firewall. In combination with Teams Phone System (the call controller/manager), they replace a PBX. This is similar to how Cisco UC Manager has a call processing server and a box like an ISR 4000 that terminates the T1 or SIP trunks. In Microsoft’s architecture, their Phone System service handles the call processing and the SBC terminates the teleco trunks. That same SBC can connect to an existing PBX (if co-existence integration is desired).

So there is a need for another box in my MDF's to connect my PBX to the MS Phone system?

If co-existence with an existing PBX is desired, an SBC in an MDF, a data center, a co-loc, or in Azure would provide that interop. If it’s an older PBXs that doesn’t support SIP, the SBC would need to be in the same room as the PBX and cross-connect with T1 cable(s). If co-existence with the existing PBX isn’t required, you can move 100% to the cloud with Phone System+Microsoft Calling Plans.

With direct routing model, if a site has SBC with 25 concurrent SIP lines, does that mean that on a teams call, only 25 users will be able to call in?

Teams conference calls actually use a phone number that terminates directly into MSFT’s cloud, so those 25 on-premises SIP lines wouldn’t be impacted by callers joining Teams meetings.

 What if you have 1,000 on prem Cisco 7841s ?

In March, 2021, Microsoft and Cisco announced that they are going to provide interoperability between several Cisco SIP phones (including the 78xx series) and Teams. Features/functionality will likely be basic, and (as of 4/22/21) there’s no firm date when the necessary “SIP Gateway” functions will be generally available.

Cisco phones

For 911 if you have the same subnets in multiple buildings, how will the PSAP know the location of the 911 call?

When a subnet spans multiple buildings (on a campus network, for instance), using the subnet to identify a physical address is inadequate. For that reason, Microsoft allows admins to upload LAN switch/port information into Teams’ Location Information Service (LIS). The LIS is a database that relates network identifiers like subnets or in this case, LAN switch ports, to the physical address where they’re located.

That allows the Teams client or phone to update the LIS when it moves… since the device will pick up a new IP address or in this case, network port when it reconnects and reregisters with Teams.

Admins upload the network information using the following cmdlets to add ports, switches, subnets, and WAPs to the LIS.

Get, Set, Remove -CsOnlineLisSubnet

Get, Set, Remove -CsOnlineLisPort

Get, Set, Remove -CsOnlineLisWirelessAccessPoint

Get, Set, Remove -CsOnlineLisSwitch

On the 911 comment can we do a crisis Listen in ?

Security desk notification is available with both Microsoft Calling Plans and Phone System Direct Routing.

You use a Teams emergency calling policy (TeamsEmergencyCallingPolicy) to configure who should be notified during an emergency call and how they are notified: chat only, conferenced in and muted, or conferenced in and muted but with the ability to unmute. You can also specify an external PSTN number of a user or group to call and join the emergency call.

For more information see

911 service is needed with five 9's for my business. Does this keep the 99.999% SLA?

Teams’ SLA is 99.9%, but the addition of the aforementioned Survivable Branch Appliance can improve that by eliminating issues of Internet / ISP network outages (provided SIP trunks are still available). Another option for some smaller locations for 911 is to drop POTS (plain old telephone service) lines in break rooms for last-resort situations.

How do you handle porting 4,000 DIDs on prem over Verizon T1s to M365 phone system?

If using Direct Routing, phone numbers can stay on the same telecom trunks as they are today, and eliminate the need to port in a traditional sense.

With Calling Plans, or if switching providers, you can plan a batched migration of numbers. This allows you to plan and scope users and training based on locations and departments. Microsoft provides a process by which you (or a partner like Enabling) request the port and then they work with the ‘losing carrier’ to schedule the port.

A wizard in the Teams Admin Center facilitates the port request. When Microsoft receives your port order, you'll get an email that verifies your request. Your request is checked and updated daily and you'll be notified of its progress and status in email. If your port request is rejected by the losing carrier, you must contact Microsoft’s PSTN service desk.

You can also view the status of your port order, in the Teams Admin Center. See for details.

Does your hosted SBC solution support integration with Twilio SIP trunking?

Is Lightpath a option for hosted direct routing?

They’re not shown on the initial list of “alpha” partners, but that doesn’t mean they’re not working on it. See the list below and more detail at

Operator Connect

SBCs are $1000+ and AD+infra. It's a big concern for SMB. I know, because I was deploy more 50+ project Skype hybrid configuration.

The hosted SBC (Operator Connect) solution offers an affordable alternative to traditional SBC connectivity. Additionally, AudioCodes will provide a hosted device you can locate on your premises that will provide your legacy service support such as PBX ATA connectivity.

Would my on prem PBX have out/inbound issues if the SBC was hosted on Azure were not available?

Yes, however, Audiocodes offers an SBC on premises with Survivable Branch Appliance (SBA) capabilities. That allows Teams devices/clients to have calling survivability when your internet goes down (provided your SIP trunks are still up).

Other direct routing FAQs were answered here. Teams Direct Routing FAQs (

How do you handle hybrid configurations and areas that still require a Physical phone?

Teams supports a variety of physical IP phones from Audiocodes, Poly, and Yealink. They’d need a common area phone (CAP) license and basic config in Teams. See

Teams can also make / take calls to legacy analog phones. Much like with Cisco ATAs, Teams also has analog gateways (from Audiocodes) that allow an analog phone to plug in, get converted to IP, and be known in Teams. The drawing below depicts the call flow.

When a user makes a call from an analog device, the signaling and media flow through the Analog Telephony Adapter (ATA) to the SBC. The SBC sends the call to a Microsoft Teams endpoint or to the Public Switched Telephone Network (PSTN) based on the internal routing table. When a device makes a call, the route it takes depends on the routing policies created for the device.

How do we get an analog line through Calling Plans?

Analog support requires Direct Routing to connect analog lines to an ATA (analog terminal adapter) / SBC device.

Is there a way to get a SIP device to connect to a Calling Plan?

There is. Teams supports a variety of physical IP phones from Audiocodes, Poly, and Yealink. They’d need a common area phone (CAP) license and basic config in Teams. See

 Is Caller ID Name supported on outbound calls and does it differ if using MS dial tone or 3rd Party dial tone?

Yes, but only in the United States. Several caveats exist with CNAM (Calling Party Name). From

“CLID & CNAM transmission is the responsibility of the terminating carrier insofar as the terminating carrier must support CLID & CNAM functionality as well as provide up to date records for both values. Microsoft reliably provides CLID values when originating calls, but those values may not be kept intact once they pass through an intermediary carrier or the terminating carrier. Unfortunately, in the event the CLID value is changed, omitted or truncated by the intermediary or terminating carrier, Microsoft has little to no recourse in correcting such problems in the public telephone network.

Inconsistencies in CNAM can be caused by delays in intermediate or terminating carriers refreshing CNAM info in authoritative databases as in the case of the United States. In countries where there is no authoritative database for CNAM, individual carrier practices can also cause problems with CNAM information arriving intact with the call. Microsoft currently does not support originating CNAM information in countries other than the United States."

 P2P calls aren't end-to-end encrypted already?

Not yet. It’s a bit of a misnomer and technicality, when you get down to it. With Teams, all calls and meetings have been and will still encrypted hop by hop, and now peer to peer calls will be encrypted end-to-end. Calls between client and SBC or client and the Teams conferencing service are encrypted, but between client/server/service, not end to end.

From, “an end-to-end encryption option for Teams 1:1 ad hoc VoIP calls will be available in preview to commercial customers planned for the first half of this year. Over the last year, we have gathered feedback from global customers, analysts, and the security community around particular industries and specific cases where end-to-end encryption (E2EE) for online collaboration might be important. To help support customer security and compliance obligations, Microsoft is planning to support E2EE for Teams 1:1 calls to provide additional option for conducting sensitive online conversations. Organizations will have the ability to enable E2EE capabilities for 1:1 ad hoc Teams VoIP calls. In order to maintain compliance and have full discretion of how E2EE is used within the company, customers will have control of who in their organization can use this capability. E2EE for 1:1 Teams ad hoc calls can only be utilized if both the caller and callee are enabled by IT and have both opted in. As we release E2EE for Teams 1:1 calls, we will continue to learn from customers how the scenarios address their needs. We will then work to bring E2EE capabilities to online meetings later. Microsoft remains committed to helping customers address security, compliance, and privacy needs with a broad portfolio of tooling.”

 Where are Calling Plans available?


Australia       (Preview customers only, through Telestra)











Puerto Rico




United Kingdom (U.K.)

United States (U.S.) & Puerto Rico

And coming this summer (2021):

New Zealand, Singapore, Romania, Czech Republic, Hungary, Finland, Norway, and Slovakia!

 Thanks for all these great questions, audience! If your questions aren’t answered here, please send an email to or reference one of the links within this FAQ.

Work with our team of Cloud Computing Consultants who have done this so many times they know all of the “minefields” to prevent missteps.