Microsoft Teams calling architecture is a three-layer licensing problem that most enterprises underestimate. Layer one: which users need Phone System (the PBX feature set). Layer two: which PSTN connectivity option delivers calls to and from the public telephone network. Layer three: how calling licences integrate with the EA without triggering the E5 bundle trap. Getting this wrong at 1,000 users costs $192,000–$336,000 per year in unnecessary spend.
This guide maps the complete Teams calling stack: Phone System licensing, the three PSTN connectivity options (Calling Plans, Operator Connect, Direct Routing), the Audio Conferencing licensing model, and the negotiation levers that reduce total calling costs by 20–35%.
Independent Advisory. Zero Vendor Bias.
500+ Microsoft EA engagements. $2.1B in managed spend. 32% average cost reduction. We design calling architectures that match your actual requirements — not Microsoft's preferred bundle.
View Advisory Services →The Three-Layer Teams Calling Stack
Teams calling requires three independent licensing elements, each with its own cost and decision logic. Understanding that these layers are separate — and can be mixed independently — is the starting point for cost-optimised calling architecture.
| Layer | What It Provides | Options | Cost Range |
|---|---|---|---|
| Layer 1: Phone System | PBX features — hold, transfer, call queues, auto attendants, voicemail | Included in E5; add-on for E1/E3 ($8/user/month) | $0 (E5) or $8/user/month |
| Layer 2: PSTN Connectivity | Dial-in/out to public telephone network | Calling Plans / Operator Connect / Direct Routing | $8–$24/user/month (Plans) to $0–$2/user/month (Direct Routing) |
| Layer 3: Audio Conferencing | Dial-in PSTN number for Teams meetings | Included in E5; add-on for E3 ($4/user/month); organiser-only requirement | $0 (E5) or $4/organiser/month |
The single most important principle: Phone System and PSTN connectivity are separate. Organisations frequently ask Microsoft for "Teams calling" and receive a proposal bundling E5 ($57/user/month) when E3 + Phone System add-on + Operator Connect delivers identical functionality at $48–$52/user/month for the subset of users who need PSTN calling.
PSTN Option 1: Microsoft Calling Plans
Microsoft Calling Plans are the simplest PSTN option — Microsoft becomes your telephone carrier. No SBC hardware, no carrier contracts, no direct routing configuration. Teams admin handles everything.
Calling Plan Tiers and Pricing
| Plan | Minutes | Price/User/Month | Best For |
|---|---|---|---|
| Domestic Calling Plan (120 min) | 120 min/month | $8 | Light callers — internal-first users |
| Domestic Calling Plan (3,000 min) | 3,000 min/month | $15 | Standard office workers |
| Domestic + International Plan | 3,000 domestic + 600 international | $24 | Workers with regular international call requirements |
| Pay-As-You-Go | Unlimited (metered) | $0 + per-minute charges | Very low volume callers |
Calling Plans: Critical Limitations
Microsoft Calling Plans are available in only 33 countries as of 2026 — a list that excludes many key markets in Asia Pacific, Latin America, and parts of Europe. Enterprises with significant headcount in Australia, Japan, Brazil, or India cannot rely solely on Calling Plans for those locations. Additionally, Calling Plans don't support analog devices, fax lines, or emergency services routing with local compliance in all markets — requirements that typically push enterprises toward Direct Routing.
PSTN Option 2: Operator Connect
Operator Connect is Microsoft's carrier integration programme: certified telecommunications carriers provide PSTN numbers and calling directly through the Teams admin centre interface. No SBC infrastructure required on the customer side — the carrier handles the gateway.
Key Operator Connect Characteristics
- Carrier list: 40+ certified carriers including BT, AT&T, Deutsche Telekom, Telstra, Orange, Verizon, and NTT. Coverage expands quarterly.
- Geographic reach: Available in 70+ countries — significantly broader than Microsoft Calling Plans.
- Management: Number assignment, porting, and billing managed through Teams admin centre. No separate carrier portal required.
- Cost model: Carrier sets per-minute or per-seat rates — Microsoft charges no additional PSTN fee beyond Phone System. Total cost typically 10–25% lower than equivalent Microsoft Calling Plans.
- SLA: Carrier-provided SLA, separate from Microsoft's M365 SLA. Verify SLA alignment before committing.
Operator Connect is the fastest-growing PSTN option in enterprise Teams deployments. For organisations with existing relationships with certified carriers, it delivers the simplicity of Calling Plans with broader geographic coverage and lower per-minute rates. The limitation: if your preferred carrier is not Operator Connect certified, you cannot use this option without a carrier change.
PSTN Option 3: Direct Routing
Direct Routing connects Teams to PSTN via a Session Border Controller (SBC) that the enterprise or its partner operates. The SBC bridges Teams to an existing carrier connection, on-premises PBX, or SIP trunk.
Direct Routing Licensing Requirements
Direct Routing has no additional Microsoft licensing cost beyond Phone System. Users need: M365 licence with Teams + Phone System (included in E5 or $8/user/month add-on). Microsoft does not charge for Direct Routing connectivity itself — the cost is the SBC hardware/software and carrier SIP trunk fees.
SBC Cost Model
SBC costs range from:
- Hardware SBC (Audiocodes, Ribbon, Oracle): $5,000–$50,000 one-time hardware + annual support, suitable for 100–5,000+ users
- Virtual SBC (cloud-hosted): $0–$500/month licensing, suitable for 50–2,000 users
- Carrier-hosted SBC (managed service): $2–$5/user/month, no capital cost, fastest to deploy
At 500 users with a $15/user/month Calling Plan, switching to Direct Routing with a virtual SBC at $1,500/month and a SIP trunk at $3/user/month saves $5,250/month ($63,000/year). The SBC setup cost is recovered in 3–6 months.
When Direct Routing Is the Right Choice
- Existing carrier contracts with favourable rates (typically 40–60% below Calling Plan rates)
- Operations in countries not covered by Calling Plans or Operator Connect
- Analog line, fax, or specialty telephony requirements
- Emergency services routing requirements with specific local compliance (911/999/112 with location data)
- Survivable branch appliance requirements (calling when internet is down)
- Migration from on-premises Lync/Skype for Business with existing SBC estate
Audio Conferencing Licensing
Audio Conferencing — the feature that provides dial-in PSTN phone numbers for Teams meeting join — is frequently misunderstood and over-licensed. The key rule: only meeting organisers need Audio Conferencing licences. Meeting participants can join via Teams client for free, or dial in to the organiser's PSTN bridge at PSTN call rates (no Audio Conferencing licence required for the participant).
Audio Conferencing is included in M365 E5. For E3 users, it's an add-on at $4/user/month. The correct licensing strategy: assign Audio Conferencing only to employees who frequently organise meetings with external participants who dial in by phone. In most enterprise populations, that's 15–40% of users, not 100%. Licensing all E3 users for Audio Conferencing when only heavy meeting organisers need it costs $4/user/month × unnecessary population.
Get an Independent Second Opinion on Your Calling Architecture
Before committing to a PSTN architecture in your next EA renewal, get an independent assessment. We evaluate all three options against your actual usage profile and geographic footprint.
Request a Consultation →The E5 Bundle Trap for Calling
Microsoft's E5 bundle ($57/user/month) includes Phone System, Audio Conferencing, and Calling Plans — making it appear to be the logical "everything calling" choice. The trap: E5 also includes security and compliance features (Defender, Purview, Entra P2) that many organisations don't need, and the Calling Plan minutes may exceed or fall short of actual usage.
The cost comparison for a 1,000-user organisation where 400 users need full PSTN calling and 600 users need only internal Teams calling:
| Scenario | Configuration | Monthly Cost | Annual Cost |
|---|---|---|---|
| E5 for all (Microsoft default) | 1,000 × E5 $57 | $57,000 | $684,000 |
| Optimised — E3 + calling for callers only | 1,000 × E3 $36 + 400 × Phone System $8 + 400 × Operator Connect ~$10 | $43,200 | $518,400 |
| Optimised — E3 + Direct Routing | 1,000 × E3 $36 + 400 × Phone System $8 + SBC + SIP trunk | ~$39,000 | ~$468,000 |
The optimised E3 + calling approach saves $165,600–$216,000 per year vs defaulting to E5 — without any reduction in calling capability for users who need it. The full Teams calling licensing framework is covered in our Teams licensing deep-dive and Teams Phone licensing guide.
EA Negotiation Tactics for Teams Calling
Teams calling negotiations have four primary leverage points that are independent of standard EA seat count discounts:
1. Separate Calling from Base Licences
In EA negotiations, Microsoft often bundles calling add-ons into the base licence count proposal to obscure the marginal cost. Always negotiate Phone System add-ons separately from E3 seat pricing — this creates a second negotiating lever and makes the calling cost visible and contestable.
2. Document Calling Plan Utilisation
Pull 90 days of calling analytics from the Teams admin centre before renewal. Most enterprises find that 30–40% of Calling Plan licences have less than 50 minutes of PSTN usage per month — qualifying for the $8 120-minute plan rather than the $15 3,000-minute plan. Downgrading these users saves $7/user/month per affected seat.
3. Introduce Operator Connect Competition
Even if you intend to stay on Microsoft Calling Plans, document a formal Operator Connect carrier evaluation. The act of requesting Operator Connect quotes from BT, AT&T, or Deutsche Telekom generates negotiating pressure that Microsoft's carrier revenue teams respond to. This approach typically yields 10–15% additional Calling Plan discount.
4. Audio Conferencing as a Trade
If your organisation uses Audio Conferencing extensively, it's a strong trade item in E5 negotiations: commit to Audio Conferencing volume in exchange for E5 pricing concessions. Conversely, if Audio Conferencing usage is low, explicitly removing it from renewal scope reduces E5 justification and supports the E3-based architecture argument.
📄 Free Guide: Microsoft EA Negotiation Playbook
Complete framework including Teams calling architecture negotiation, PSTN option comparison, and E5 vs E3 bundle analysis.
Download Free Guide →Frequently Asked Questions
What are the three Teams PSTN connectivity options?
The three options are: (1) Microsoft Calling Plans — Microsoft provides PSTN directly, available in 33 countries, simplest to deploy, highest per-minute cost; (2) Operator Connect — certified carriers provide PSTN via Teams admin interface, available in 70+ countries, no SBC infrastructure required; (3) Direct Routing — enterprise connects existing SBC/PBX to Teams via SIP, available globally, lowest per-minute cost, highest infrastructure complexity.
Does Teams Phone System come with PSTN calling?
No. Teams Phone System (the licence that enables PBX features — call queues, auto attendants, hold/transfer) does not include PSTN calling. Phone System is included in E5 and available as an add-on for E3 at $8/user/month. PSTN connectivity is separate and must be added via one of the three options.
When should an enterprise choose Direct Routing over Calling Plans?
Direct Routing is preferable when your organisation operates in countries not covered by Microsoft Calling Plans, has existing SBC infrastructure or carrier contracts with favourable rates, needs per-minute calling costs minimised at scale (typically above 500 active callers), or requires specific telephony features that Calling Plans don't support. The infrastructure cost of an SBC is typically recovered within 6–12 months for organisations above 250 active callers.
What is Operator Connect and when is it the right choice?
Operator Connect lets certified carriers provide PSTN connectivity directly within the Teams admin centre — no SBC hardware required. It's the right choice for organisations that want to keep their existing carrier relationship (if certified), need coverage in countries where Microsoft Calling Plans aren't available, and want simpler management than Direct Routing without the higher cost of Microsoft-provided Calling Plans.