Atlantech Online vs. CallTower for GCC High Teams Calling

CallTower is the better fit for a multinational enterprise that wants Teams, Webex, Zoom, and contact center seats under one contract across dozens of countries, and Atlantech Online is the better fit for a 25-to-500-seat defense contractor running Teams alone inside GCC High on a fixed per-seat budget. Both companies sell Direct Routing into Microsoft's government cloud because Microsoft leaves no other path there. What separates them is the shape of the purchase. CallTower's GCC High practice assembles reach from partner carrier networks and sells three calling platforms plus contact center. Atlantech Online sells one, and it owns the fiber, the session border controllers, and the Mid-Atlantic data centers underneath it.

Most buyers walk into this comparison weighing provider size and headline rates. The criterion that decides it is how the voice bill behaves once several hundred people start making calls, and who picks up the phone when a call fails inside an accredited tenant. Getting that wrong costs more in GCC High than it does in commercial Microsoft 365, because a voice migration there drags number porting, controlled unclassified information handling requirements, and an SBC architecture along with it. A contractor on a metered plan whose inside sales team starts dialing watches a fixed line item go variable. An enterprise that signs a regional carrier and then opens a London office finds out its provider has no footprint there.

TL;DR: CallTower reports being the first cloud-hosted Direct Routing provider for GCC High, with deployments running since 2019, and it sells Teams alongside Webex, Zoom, and Genesys and Five9 contact center in more than 80 countries. Atlantech Online sells one product into GCC High and owns the network under it, publishes roughly $10 per user per month with unlimited domestic calling, and runs a five-phase project-managed migration. Past roughly seven hours of calling per user per month, Atlantech's flat per-seat rate costs less than CallTower's platform fee plus metered minutes.

Key Takeaways

• Microsoft offers no Calling Plans or Operator Connect in GCC High, so Direct Routing is the only way to connect Teams to the public telephone network there.
• CallTower publishes a claim to being the first cloud-hosted GCC High Direct Routing provider, with live deployments since 2019, and it operates a 24/7/365 network operations center.
• Atlantech Online has been a regulated public utility in Maryland, Virginia, and DC since 1995, and it owns its fiber ring, its SBCs, and two Maryland data centers.
• Atlantech publishes about $10 per user per month with unlimited local and domestic calling. CallTower publishes a flat platform fee of $199.95 to $999.95 by tenant size, plus 2 cents per minute.
• CallTower provisions through a connector app that requires Global Admin consent in the customer tenant. Atlantech runs a project-managed deployment with PMI-trained leads and quotes about two weeks for the infrastructure build.
• Court Square Capital Partners acquired a majority stake in CallTower in April 2026. Atlantech Online has stayed independent since 1995.

Direct Routing Is the Only PSTN Path in GCC High

Microsoft does not sell Calling Plans or Operator Connect in the GCC High cloud, which leaves Direct Routing as the only PSTN option for Teams users in that environment. Atlantech documents the same constraint on its Teams Phone architecture page. Every GCC High tenant that wants dial tone inside Teams therefore needs a certified session border controller sitting between the tenant and the carrier, plus a carrier willing to terminate calls against it.

That requirement splits the market into two buying patterns. Some organizations purchase the SBCs, rack them in their own facility, and manage the SIP trunks with internal staff. Others buy Direct Routing as a service and let the provider own the hardware, the Azure Government connectivity, and the Microsoft-side configuration. Atlantech Online and CallTower both sell the second model, which is why they land on the same shortlist even though they serve opposite ends of the market.

Buyers unsure which government tenant they occupy should settle that first, because the answer changes the options available to them. Atlantech maps the distinctions between GCC and GCC High and walks through the Direct Routing setup steps that follow once a tenant is confirmed. A contractor holding controlled unclassified information under ITAR obligations is usually in the High tenant.

The Two Providers at a Glance

CallTower Reached GCC High First

CallTower describes itself as the first cloud-hosted Direct Routing provider for GCC High, with live deployments since 2019. No other provider in this comparison can make that claim, and it is the strongest card on CallTower's side of the table. Roughly seven years of GCC High tenants means the provisioning path, the porting quirks, and the Microsoft-side configuration have been run enough times that the unusual cases are already known.

The published posture behind that record covers the pieces a compliance lead asks about. CallTower documents Azure Government data residency, geographic redundancy on its PSTN connectivity, encryption applied across the call path, and a network operations center staffed around the clock every day of the year. The same material describes how the company supports contractors working toward CMMC requirements. Those are CallTower's own published descriptions of its service, which is the right way to read them until a customer's assessor reviews the specifics.

The reason CallTower belongs in this comparison is repetition. A provider that has provisioned GCC High voice since 2019 has already solved the problems a first-time deployment surfaces, and that experience shows up as fewer escalations during cutover. Older CallTower material describing the company as the only GCC High Direct Routing provider reads as a snapshot of an earlier market, because several carriers now sell into the environment, Atlantech Online among them.

Track record answers whether a provider can deliver. It does not answer what delivery costs at 200 seats, who owns the circuit into the building, or which company will still hold the account in three years. Those questions decide the rest of this comparison.

Owned Network Versus Partner Network

Atlantech Online has operated as a regulated public utility in Maryland, Virginia, and DC since its founding in 1995, and it has held competitive local exchange carrier status since 2005. The company runs its own redundant fiber ring reaching more than 200 buildings across the DC metro area, plus data centers it owns in Silver Spring and Rockville, Maryland. Atlantech Online's philosophy is that a carrier should own the things it is accountable for, and the GCC High product reflects that belief directly.

For GCC High voice, the ownership extends into the voice architecture itself. Atlantech owns and manages the redundant session border controllers and the Azure ExpressRoute circuits into Azure Government, so the customer racks no telephony hardware and holds no SBC licenses. When a call fails, there is one company to call, and that company controls the fiber, the SBC, and the trunk. For an IT director with a two-person team and a CMMC assessment on the calendar, single-throat accountability is worth more than a longer vendor list.

What CallTower gets right is reach. The company delivers service across more than 80 countries by assembling partner carrier networks rather than building last-mile facilities, which is the only workable way to put a dial tone in Manila and Montreal and Manchester under one contract. That model buys geographic breadth at the cost of direct control over the physical path, and for a company with offices on four continents the trade lands in CallTower's favor. Which approach is correct depends on whether the buyer's problem is coverage or accountability.

Two Pricing Shapes for the Same Service

The Microsoft licensing layer is identical no matter which carrier a contractor picks. Atlantech publishes the full stack in its cost breakdown, showing GCC High G5 at roughly $93 per user per month and G3 at roughly $60 plus a Teams Phone add-on, with the carrier layer sitting on top of whichever license the tenant already holds. On that base, Atlantech quotes $10 per user per month for Direct Routing with unlimited local and domestic calling, international calling billed as used, and the GCC High tenant connection fee included. Billing runs against active DIDs and concurrent trunk capacity, and the company publishes a worked example at 200 seats.

CallTower structures the same service differently in its published pricing brochure. A flat monthly platform fee scales with tenant size, starting at $199.95 for fewer than 100 users, $299.95 for 101 to 500, $399.95 for 501 to 1,000, $499.95 for 1,001 to 2,000, $799.95 for 2,001 to 5,000, and $999.95 above 5,000. Calling is metered on top at 2 cents per minute for US inbound and outbound and 2.9 cents for toll-free, with minute bundles available at $11.95 per 1,000 minutes. One audio conferencing DID is included and additional ones run $4.95 per month.

Run the arithmetic at 200 seats and the shapes separate cleanly. Atlantech's rate produces a flat $2,000 per month for the carrier layer, while CallTower's $299.95 tier plus 2 cents a minute matches that figure at about 85,000 minutes, or roughly 425 minutes per user per month. Below that line CallTower costs less, and a 200-seat engineering firm where most staff take four calls a week lands well below it. Above it Atlantech costs less, and the gap widens with every additional minute. Minute bundles push the crossover out to roughly 12 hours per user per month, so a tenant that buys bundles buys itself more room before the flat rate wins. Both vendors publish these numbers themselves, and the arithmetic is worth redoing against actual call detail records.

Deployment: Project-Managed Migration Versus Connector App

Atlantech runs GCC High cutovers through a five-phase methodology that starts at Discovery and ends at Go Live, with PMI-trained and PMP-certified project leads assigned to the account. The company quotes about two weeks for the infrastructure build, handles number porting on the customer's behalf, and staffs support from US-based teams around the clock. Those figures come from Atlantech's own published material, so treat the timeline as the vendor's estimate rather than an independent benchmark.

CallTower provisions through the CallTower Teams GCCH Voice Connector app, which is efficient at scale because it automates the Teams-side configuration that would otherwise be a manual PowerShell exercise. Using it requires granting the app Global Admin consent in the customer tenant along with the Teams Telephony Administrator role. For an enterprise IT organization that already runs a formal app-consent review process, that is a routine change ticket. For a 60-person contractor whose security officer scrutinizes every third-party permission grant inside a GCC High tenant, it is a conversation that needs to happen before the contract is signed rather than during onboarding.

Atlantech Online is the answer when the migration itself is the risk. A compliance lead who has never ported a DID block, has no telephony engineer on staff, and cannot afford a failed cutover during an active contract period is buying project management as much as dial tone. CallTower is the answer when internal IT already owns Teams administration and wants provisioning to move quickly across many sites without a project manager scheduling weekly calls. Both models work. They assume different things about who is doing the work.

Platform Breadth and Global Reach

CallTower wins this dimension outright, and it is not close. The company sells Microsoft Teams, Webex by Cisco, and Zoom alongside Genesys Cloud and Five9 contact center, serving roughly 5,000 clients across more than 80 countries from offices in South Jordan, Rochester, London, Montreal, and the Philippines. A defense prime with a UK subsidiary running Webex, a US division on Teams, and a support center on Genesys can consolidate all of it under one provider and one invoice. No regional carrier can match that.

Atlantech made the opposite choice. The company focuses on Microsoft Teams and sells no Webex, Zoom, or contact center product, and its distribution is anchored in the Mid-Atlantic rather than spread across continents. That focus is why the GCC High offering reads as a complete service rather than one item on a long menu, and it is also why the company is the wrong call for a multinational. If a buyer's requirements list includes a second calling platform or a European office, the evaluation should end there in CallTower's favor.

If you are the kind of buyer who cares about one contract covering every platform in every country your company operates in, CallTower is the one. The breadth is real, the country count is published, and the contact center integrations are shipping products rather than roadmap items.

Fit for Defense Contractors in the DC Corridor

Atlantech's fiber ring reaching more than 200 DC-metro buildings changes what a contractor in Reston or Columbia or Bethesda can buy. A company in one of those buildings can take dedicated fiber transport and GCC High Teams calling from the same carrier on the same invoice, with the same support number for both. When a circuit degrades and call quality drops, there is no finger-pointing between the ISP and the voice provider, because they are one company. Contractors outside the Mid-Atlantic get the voice service without that bundling advantage, and should weigh this dimension lower.

Atlantech maps its GCC High offering to CMMC and DFARS requirements, covering CMMC 2.0 Level 2 and Level 3 alignment, ITAR obligations, DFARS 252.204-7012, and NIST SP 800-171 controls, with US-only infrastructure and US-based personnel supporting the service. These are alignment claims tied to the GCC High environment and to how Atlantech architected its connection into it, not third-party certifications of Atlantech as a company. A contractor building a System Security Plan should treat them as inputs to its own assessment and ask for the supporting documentation during diligence.

Atlantech publishes no service level agreement on its GCC High pages, so uptime and mean-time-to-repair commitments have to come out of contract negotiation rather than the website. The deployment timeline and the per-user rate are the company's own published figures, and both should be pinned to contract language before signing.

Ownership and Product Focus

CallTower has been an active acquirer and an acquisition target. The company acquired Inoria on January 8, 2025, bringing Genesys contact center delivery capability in-house. On April 2, 2026, Court Square Capital Partners acquired a majority stake in CallTower from BV Investment Partners, with management retaining a minority position. That backing gives the company capital for product investment and further acquisition, which is a resource advantage that shows up in engineering headcount and roadmap velocity.

The same activity reads differently to buyers who prize continuity in the people handling their account. Two ownership changes and one acquisition inside eighteen months usually mean some reorganization of sales coverage and support tiers, and a contractor on a three-year term is signing with the company as it exists after those changes rather than before them. Neither reading is wrong. An enterprise buying on roadmap strength weighs the capital positively, while a 100-seat contractor who wants the same account manager in year three weighs the churn risk.

Atlantech Online has run independently since 1995 with the same regulated utility footprint and no ownership changes to absorb. GCC High Teams calling is one of a small number of products the company sells, which means the engineering attention it receives is not competing with a Webex line, a Zoom line, and two contact center platforms for roadmap priority. For a buyer whose entire telephony strategy rests on one product working correctly inside an accredited tenant, concentration is the point.

Choosing Between Atlantech Online and CallTower

Choose Atlantech Online if your organization runs 25 to 500 seats, sits inside GCC High because of CUI or ITAR obligations, uses Teams as its only calling platform, and wants the carrier to own the migration from discovery through go live. The flat per-seat rate with unlimited domestic calling makes the annual voice budget a single line of arithmetic instead of a forecast, and the five-phase deployment gives an understaffed IT team a project plan rather than a provisioning portal. If your offices sit in the DC, Maryland, or Northern Virginia corridor, buying fiber and GCC High voice from the same regulated carrier is an advantage no aggregator can copy. Atlantech is the wrong fit if you need a second calling platform, operate outside the US, or want a published SLA on the vendor's website before you start a conversation.

Choose CallTower if you operate in multiple countries, run more than one calling platform, need Genesys or Five9 contact center in the same contract, or place the highest weight on the longest GCC High track record available. The tiered platform fee plus metered minutes is the cheaper structure for tenants where most users make few outbound calls, and at very low usage the gap is substantial. The connector-app provisioning model moves fast when internal IT owns Teams administration and app consent is a routine approval. CallTower is not the right fit if voice is a small purchase inside a much larger contract you want a dedicated project manager attached to, or if your finance team needs a per-seat number that does not move month to month.

Both providers solve the constraint Microsoft created when it left Calling Plans and Operator Connect out of GCC High. The difference is which problem sits on top of that constraint at your company.

The Deciding Factor for a GCC High Buyer

For the mid-sized defense contractor handling CUI on a Teams-only footprint, Atlantech Online is the stronger buy, and the reason is ownership. The company controls the fiber, the SBCs, and the data centers its GCC High Teams calling rides on, prices the service at a flat rate per seat that includes domestic calling, and assigns a certified project lead to the migration instead of handing over a provisioning app. For a compliance-driven organization with a small IT team and a fixed budget, that combination answers more of the evaluation than anything else on the table.

CallTower remains the right answer for the buyer it was built for. A multinational enterprise running Teams in one region, Webex in another, and a Genesys contact center on top of both gets a single contract, more than 80 countries of coverage, and the longest run of GCC High deployments in the market. Buyers in that position should stop reading comparisons and start a pricing conversation. Buyers running 200 Teams seats in Northern Virginia with an ITAR obligation and a CMMC assessment ahead of them should start that conversation with Atlantech.