Direct Routing vs Operator Connect vs Calling Plans: A Field Guide from 100+ Deployments

After deploying Microsoft Teams voice across more than 100 global enterprises — from 50-seat law firms to 90,000-seat financial institutions — I have seen every permutation of what works, what breaks at 2 AM on a Friday, and what nobody warns you about in the Microsoft documentation. This is the field guide I wish someone had handed me before deployment number one.

Let me be direct: there is no universally correct answer. Each approach — Direct Routing, Operator Connect, and Microsoft Calling Plans — occupies a specific niche, and the right choice depends on factors that most comparison articles gloss over entirely.

Architecture & Call Flow: Understanding What Actually Happens to Your Packets

Direct Routing

In Direct Routing, your Session Border Controller (SBC) establishes a persistent TLS/SRTP connection to the Microsoft 365 Phone System via FQDN-based SIP trunking. The call flow for an outbound PSTN call traverses:

Teams Client → Microsoft Transport Relay → Phone System → SIP Proxy (sip.pstnhub.microsoft.com) → Your SBC → SIP Trunk → PSTN Carrier

The critical detail: with Local Media Optimization (LMO) or Media Bypass enabled, the RTP stream flows directly between the Teams client and the SBC, bypassing the Microsoft media processors entirely. This matters enormously for latency-sensitive deployments.

What the documentation undersells: the SIP signaling always traverses Microsoft's infrastructure, even with Media Bypass. Your SBC must maintain connectivity to all three Microsoft SIP proxies and handle failover between them.

Operator Connect

With Operator Connect, your operator's SBC peers with Microsoft directly through the Operator Connect program:

Teams Client → Microsoft Transport Relay → Phone System → Operator's SBC (Microsoft-peered) → Operator's PSTN Network

You never touch the SBC. The trade-off is absolute: you gain simplicity and you lose control.

Microsoft Calling Plans

Calling Plans represent the most abstracted model. Microsoft becomes your PSTN carrier:

Teams Client → Microsoft Transport Relay → Phone System → Microsoft PSTN Infrastructure

There is no SBC in the picture at all.

SBC Requirements: The Component That Changes Everything

Number Management: Who Owns Your Numbers Matters More Than You Think

The number ownership question is where I see the most regret in enterprises that chose Calling Plans without understanding the implications. When Microsoft holds your numbers and you later decide to migrate, the porting process is governed by Microsoft's timelines.

Cost Analysis: The Numbers Behind the Numbers

Direct Routing — Real Cost Breakdown

The Hidden Costs of "Free" Calling Plans

Communication Credits are required for toll-free and overage

International rates on Pay-As-You-Go can be staggeringly expensive

Number acquisition is limited to Microsoft's inventory

No survivability — if Teams is down, PSTN is down

Reliability & Failover: Who Controls Your Dial Tone

Direct Routing is the only model that gives you genuine survivability during a Microsoft 365 outage. For regulated industries — healthcare, emergency services, financial trading floors — this is not optional.

What Nobody Tells You About Direct Routing

Certificate management is an ongoing operational burden. I have responded to emergency calls from organizations whose Direct Routing stopped working at 3 AM because a certificate expired and nobody had monitoring in place.

SBC firmware updates are not optional and not risk-free. Microsoft periodically updates the SIP interface behavior, and SBC vendors release firmware to maintain compatibility. Build a lab SBC to test firmware before production.

Call quality monitoring has gaps. The Microsoft CQD tells you almost nothing about what happens between your SBC and the carrier. You need SBC-side monitoring and ideally synthetic call testing.

When Operator Connect Actually Makes Sense

Operator Connect is right when ALL of these are true:

Your preferred operator participates in the OC program

You don't need SBC-level customization

You want to offload SBC operations entirely

Compliance can be met with Teams-native recording

You have a strong existing relationship with a participating operator

My Recommended Decision Framework

Scalability: From 10 Users to 100,000

At enterprise scale, Direct Routing almost always wins on cost because SIP trunk pricing scales far more favorably than per-user licensing.

Final Thoughts

My advice: do not make this decision based on a feature comparison matrix alone. Run a proper cost model with your actual calling patterns. Assess your compliance requirements. Evaluate your IT team's appetite for SBC operations. Plan for the next 3-5 years.

Whichever model you choose, the dial plan and voice routing configuration is where most deployments get bogged down. SwiftM365 can generate the dial plans and voice routing policies for any of these approaches, saving hours of manual configuration.

---

Have questions about choosing the right Teams voice model? Reach out via our feedback page or contact me directly at +91 9011070193.