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Microsoft Teams Voice

Chamara Priyadarshana

What is Teams Phone & how PSTN calling works

Teams Phone adds cloud PBX capabilities (voicemail, auto attendants, call queues, caller ID, etc.). To make and receive external calls (PSTN), you choose one (or a mix) of these connectivity options: Calling Plans, Operator Connect/Teams Phone Mobile, or Direct Routing (via an SBC you control).

Microsoft’s official setup roadmap breaks deployment into clear stages: buy/assign licenses, pick PSTN connectivity, get numbers, configure emergency calling, set up auto attendants/call queues, and then manage & optimize.


A Use Case:

A customer dials your main number → Auto attendant plays a greeting and offers 1. Sales / 2. Support → choosing Support sends the caller to a call queue that rings the next available agent → if nobody answers, a shared voicemail captures the message and emails it to the Support group’s mailbox. All of this is configured in Teams Phone’s PBX features; the call reached you from the public network through your chosen PSTN option.

1) End‑to‑end setup (the high‑level path)

  1. Buy & assign a Teams Phone license to each user who will use calling features. Then “voice‑enable” the user (TAC or PowerShell).
  2. Choose PSTN connectivity: Microsoft Calling Plans, Operator Connect/Teams Phone Mobile, or Direct Routing (SBC).
  3. Get and assign phone numbers (from Microsoft, your operator, or upload Direct Routing numbers).
  4. Set up emergency calling and dynamic emergency addresses per your region’s rules.
  5. Configure voice apps (Auto Attendants, Call Queues) and user policies (calling, voicemail, caller ID).
  6. Validate & manage: monitor SLOs like call success rate, p95 setup time, and adjust routing/policies as needed. Microsoft’s voice solution guidance provides planning and deployment context.

2) Assign licenses & create accounts (users and resource accounts)

  • User licensing: Assign Teams Phone (and, if needed, Calling Plan or Operator Connect). Don’t give Calling Plan if you use on‑prem PSTN (Direct Routing). Use the Microsoft 365 admin center or PowerShell for single or bulk assignment.
  • Resource accounts (for Auto Attendants/Call Queues): assign the Teams Phone Resource Account license (zero‑cost) — don’t assign Teams Phone Standard to resource accounts.
  • License changes can impact numbers: removing prerequisite licenses can unassign phone numbers and disable PSTN calling until corrected.

3) Policies & settings: the core levers

  • Calling policies decide what users can do: private calls, call forwarding, voicemail, delegation, busy options, spam filtering, and more (set globally or per‑user).
  • Voicemail policies control transcription, profanity masking, prompt language, and max recording duration.
  • Voice applications policies let you delegate Auto Attendant/Call Queue configuration to authorized users (least‑privilege), optionally with Teams Premium for advanced capabilities.
  • Policy assignment precedence: a user has one effective policy per type; direct assignment overrides group; group ranking resolves ties.
  • Reference for all policy types lives in the Teams settings & policies reference.

4) Frontline scenarios: shared & personal devices

For shift‑based teams using shared devices, Shared Device mode (Entra ID) enables single sign‑in/out across supported apps, reducing data leakage risk when devices are handed over between workers. Use Microsoft’s frontline guidance to plan shared or BYOD deployments and onboarding flows.

Microsoft also provides a frontline Teams onboarding experience (public preview) that guides workers through MFA, Authenticator/Company Portal setup, and app protections for personal devices.

5) Security: Enhanced Encryption (E2EE) policy

Teams encrypts data in transit and at rest by default. For one‑to‑one unscheduled calls, you can permit end‑to‑end encryption (E2EE) — a stricter mode that removes access for services like recording/transcription during the call. Admins govern availability via Teams Enhanced Encryption Policy, and users can enable it if allowed.

Create or adjust enhanced encryption policies with PowerShell (e.g., New‑/Set‑CsTeamsEnhancedEncryptionPolicy) for calls and, with Teams Premium, for sensitive meetings.

For a broader security posture reference (TLS/SRTP, threat mitigations), see the Teams security guide.

6) Voice routing policy (Direct Routing)

If you use Direct Routing, Teams selects an SBC based on voice routes and PSTN usages, packaged into a voice routing policy (also called call routing policy). Assign these policies to users who should place calls via your SBC(s).

Microsoft’s Direct Routing guidance outlines the four setup steps: connect SBC, enable users, configure call routing, and (optional) translate numbers. It also lists support boundaries and certified SBC requirements.

Tip: Be careful with the Global voice routing policy — applying it org‑wide can inadvertently route Calling Plan/Operator Connect users through your Direct Routing trunk if there’s a pattern match. Prefer custom policies for specific populations.

7) What is a SIP trunk (in Teams context)?

In Teams Direct Routing, your Session Border Controller (SBC) terminates telephony trunks (typically SIP) on one side and connects to Microsoft’s SIP proxy on the other. Teams documents describe how SIP is implemented (headers, OPTIONS/INVITE flows) and that the SBC must be certified and paired to your tenant. In short: a SIP trunk is the operator or PBX interconnect your SBC uses to reach the PSTN and/or other telephony gear.

8) Auto Attendant — what it is & how to configure it

Auto Attendants provide menu‑driven call routing (“For Sales, press 1…”) with time‑of‑day/holiday logic, directory search, speech recognition, and destinations such as people, call queues, operators, external numbers, or shared voicemail. They’re built in the Teams admin center or via PowerShell and rely on resource accounts.

Configuration steps (TAC): create a resource account (+ license), define language/time zone, business/after‑hours/holidays, menu prompts, operator (recommended), and destinations; then assign a number to the resource account if external callers must reach it. PowerShell is available for advanced scenarios.

You can also delegate Auto Attendant/Call Queue changes to authorized users via voice applications policies — and optionally enable the Queues app with Teams Premium for richer delegated management.

9) Caller ID (CLID/CNAM) and Caller ID policies

Caller ID policies let you:

  • Present the user’s direct number, a resource account number (e.g., main line), or anonymous;
  • Set company name (where supported);
  • Block inbound PSTN caller ID for users;
  • Allow user override where appropriate. Configure these with the Teams admin center or PowerShell (New‑CsCallingLineIdentity).

Microsoft explains how CLID/CNAM behave across carriers and regions: CLID is typically reliable; CNAM support varies by country and by the terminating carrier’s databases and refresh cadence. Expect variability, especially outside the U.S.

Related calling policy settings (spam filtering, busy options, voicemail routing) complement caller ID behavior for inbound/outbound flows.

10) Number management & porting

If you’re using Microsoft Calling Plans, you can transfer (port) existing numbers from your current carrier into Teams using the porting wizard (TAC), with country‑specific LOA requirements and timelines. Microsoft’s “What’s a port order?” guide explains the process and data you’ll need (CSR, invoices, BTN, etc.). Region pages (e.g., U.S.) list SLAs and details.

For Direct Routing, you acquire/port numbers with your PSTN partner and then upload/manage those numbers in Teams for assignment.

Change control note: Removing required licenses from a user with an assigned number can unassign that number; make licensing changes atomically to avoid call disruption.

11) Operator Connect & Teams Phone Mobile (optional paths)

You can also connect to the PSTN via Operator Connect and Teams Phone Mobile with supported operators, manage numbers in TAC, and assign them to users. (The flow includes enabling an operator, assigning numbers and emergency addresses, and managing operator relationships.)

PSTN (Public Switched Telephone Network)

The global “traditional phone network” that lets you dial real phone numbers (landlines/mobile). Teams Phone connects to the PSTN using Calling Plans, Operator Connect/Teams Phone Mobile, or Direct Routing.
Example: Your sales rep dials +94 11 2xxx xxx from the Teams client. Because your tenant has PSTN connectivity, the call leaves Microsoft 365 and reaches the customer’s mobile through the public phone network.

What PBX capabilities include

  • Auto attendants (IVR menus) – Callers hear options (“For Sales, press 1…”) and are routed by keypress or speech; works with business hours/holidays and can route to users, queues, external numbers, or shared voicemail.
  • Call queues (hunt groups) – Put callers in line, play hold music, and ring the next available agent; use together with auto attendants for front‑door call flow.
  • Voicemail (personal & shared) – Voicemails are delivered to Exchange mailboxes; admins can control transcription, profanity masking, and languages; shared voicemail lets a team access a common mailbox.
  • Call controls – Users can transfer, forward, and place 1:1 or group calls from any Teams client or certified phone device.
  • Call park & group call pickup – Park a call to a retrieval code; colleagues in a call group can pick up calls for one another with controlled notifications and policies.
  • Dial plans & extensions – Normalize how users dial (e.g., 4‑digit extensions) into standard E.164 numbers for routing; create tenant dial plans and rules.
  • Caller ID management (CLID/CNAM) – Set outbound caller ID to user, service (resource account) number, anonymous, or block inbound caller ID via policy.
  • Emergency calling (E911) – Configure emergency addresses and dynamic location‑based routing/notifications that follow the user’s network location.
  • Admin & device support – All PBX features are managed centrally in the Teams admin model and work with certified desk phones and peripherals.

PBX vs. PSTN (how user reach the outside world)

  • PBX capabilities = the features for handling calls inside your tenant (menus, queues, voicemail, policies, etc.).
  • PSTN connectivity = the path to public phone numbers so you can call mobiles/landlines. In Teams you choose Calling Plans, Operator Connect/Teams Phone Mobile, or Direct Routing (via an SBC).

TAC (Teams admin center)

The web portal where admins configure all Teams settings—users, numbers, policies, voice routing, auto attendants, etc.
Example: You go to TAC → Voice → Calling policies to turn on call forwarding for a specific group of users.

SBC (Session Border Controller)

A specialized voice firewall/interop device you (or your carrier) manage to connect your phone carrier or legacy PBX to Teams via Direct Routing. It terminates SIP trunks on one side and the Microsoft SIP proxy on the other.
Example: You already have a telecom contract. You deploy a certified SBC, connect it to Microsoft’s Direct Routing, and your users place/receive PSTN calls through that SBC instead of a Microsoft Calling Plan.

SLOs (Service Level Objectives)

Internal reliability/quality targets you set—e.g., “≥99.9% call setup success,” “p95 audio join time ≤ 8s,” “MOS ≥ 4.0.” (This term is general to SRE/ops; you’ll track them using Teams/Call Quality dashboards and your own observability.)
Example: You decide that if weekly error budget burn for call failures exceeds 15%, you pause new routing changes.

E2EE (End‑to‑End Encryption)

Extra‑secure encryption where only the two endpoints can decrypt the media. In Teams, you can allow E2EE for one‑to‑one, unscheduled calls (and with Teams Premium, certain meetings). It disables features like recording and transcription while active.
How to allow it: Admins create/assign a Teams Enhanced Encryption Policy (PowerShell: New/Set‑CsTeamsEnhancedEncryptionPolicy) so users can turn E2EE on for their 1:1 calls.
Example: Legal counsel and a VP toggle E2EE for a sensitive 1:1 call; recording and captions are unavailable during that call by design.

SIP trunk

A phone service connection using the SIP protocol. In Direct Routing, your SBC connects to a carrier or PBX over a SIP trunk, and to Microsoft’s SIP proxy for Teams.
Example: Your carrier delivers 100 DIDs over a SIP trunk to your SBC. The SBC then routes those numbers to Teams users via Direct Routing voice routes.

CLID / CNAM (Caller ID number & name)

CNAM = the name shown (when supported by the terminating carrier/region). Behavior depends on policy settings and carrier databases.
What you can control: Create Caller ID policies to present the user’s own number, a resource account number (e.g., main line), anonymous, or block inbound caller ID. PowerShell: New‑CsCallingLineIdentity.
Example: Your support team places outbound calls but you want customers to see the main support number and “Contoso Support.” Assign a Caller ID policy that substitutes the resource account’s number and sets company name (where supported).

CLID = the phone number shown to the person you call.

Useful Links:

References (Microsoft Docs)

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