WiFi Calling in Buildings: How to Solve Mobile Dead Zones in Australian Commercial Properties

Mobile dead zones are not a minor inconvenience. For a commercial building manager, they are a leasing liability. For a tenant, they mean dropped calls, missed clients, and staff stepping outside to make basic phone calls. For a strata committee, they generate complaints that have no easy answer — until recently.

WiFi calling has changed the equation. All three major Australian carriers now support it, every modern smartphone ships with it enabled, and a well-designed building WiFi network can deliver reliable mobile coverage to basements, car parks, lift lobbies, and plant rooms without a multi-hundred-thousand-dollar antenna system. This article explains how it works, what your building needs to support it, and where the technology has genuine limits.

Why Australian Buildings Have Mobile Dead Zones

The physics of radio frequency propagation through dense construction materials is straightforward: the denser the material, the greater the signal loss. Australian commercial buildings, particularly those constructed from the 1970s onward, are built for structural performance, fire resistance, and thermal efficiency — all properties that correlate poorly with mobile signal penetration.

The Materials That Kill Mobile Coverage

Reinforced concrete is the primary culprit. Research on construction material attenuation shows that a single concrete wall can impose signal loss of between 25 and 35 dB depending on thickness and mix. Reinforcing steel within the slab compounds this, creating a Faraday-cage effect that reflects and absorbs radio frequency energy. A multi-storey building with a below-grade car park effectively places several of these barriers between the outdoor base station and anyone inside.

The problem intensifies with:

• Lead-lined glass — used in some curtain-wall commercial facades and in medical buildings. Attenuation losses can exceed 40 dB, making the glass itself as impenetrable as a concrete wall.
• Metalised low-emissivity (Low-E) glass — common in energy-efficient commercial glazing. The metallic coating that improves thermal performance also blocks radio signals, reducing penetration by 20–40 dB across mobile frequency bands.
• Steel structural elements — lift shafts, stairwell enclosures, and plant room walls built from steel sheeting or surrounded by structural steel frames create enclosed environments that outdoor tower signals cannot reach.

The Worst Areas in Any Building

Certain building zones consistently produce dead zones regardless of the carrier or the device:

Basements and car parks. Below-grade spaces are surrounded by concrete on all sides with no line of sight to any outdoor antenna. Even the strongest outdoor signal from Telstra, Optus, or TPG cannot penetrate multiple floors of reinforced concrete.

Lift cores and shafts. Steel lift cars moving through steel-lined shafts create a near-total RF blackout. Calls drop the moment a person enters a lift.

Stairwells. Internal stairwells, particularly in the core of a building with no exterior wall exposure, sit in a coverage shadow.

Plant rooms and comms rooms. Often located in basements or service floors, these spaces are constructed from solid concrete or masonry and have no windows. Staff working in plant rooms routinely have no mobile connectivity.

Interior rooms far from exterior walls. In deep-floorplate commercial buildings — common in CBD towers built from the 1990s — the centre of each floor can be 20 or more metres from any external glazing. Signals that penetrate the facade lose 10–15 dB per internal wall, leaving the building core in a signal shadow.

All Three Major Australian Carriers Are Affected

The networks most Australians rely on — Telstra (850 MHz, 1800 MHz, 2100 MHz, 700 MHz, 2600 MHz), Optus (900 MHz, 1800 MHz, 2100 MHz, 700 MHz), and Vodafone/TPG (900 MHz, 1800 MHz, 2100 MHz) — all transmit on frequencies that attenuate significantly through dense construction. Higher frequency bands (2100 MHz and above) that carry the bulk of 4G and 5G data traffic are particularly susceptible to penetration loss. Lower frequency bands (700–900 MHz) penetrate better but are typically reserved for coverage extension in rural areas and are not the primary workhorse in urban environments.

The result is that mobile dead zones in Australian commercial buildings are a structural problem, not a carrier problem. No single carrier has a building penetration advantage, and switching carriers does not solve the problem.

What WiFi Calling Is

WiFi calling — also called VoWiFi (Voice over WiFi) — is a feature built directly into the operating system of modern smartphones that allows voice calls, SMS, and MMS to be routed over an internet connection rather than a cellular network when the cellular signal is insufficient.

To the person making the call and the person receiving it, a WiFi call is indistinguishable from a standard mobile call. It appears on the recipient's screen as a normal incoming call from the caller's mobile number. There is no separate application to download, no account to create, and no number to register. The feature is native to the device operating system and activates automatically when the cellular signal drops below a usable threshold.

Carrier Support in Australia

All three major Australian carriers support WiFi calling for their customers:

• Telstra supports WiFi calling across its prepaid and postpaid plans, and since late 2022 has extended this support to MVNOs operating on the Telstra network. Customers on Telstra-network MVNOs (including Boost, Woolworths Mobile, and others) can use WiFi calling without opting in — it activates based on device compatibility.
• Optus supports WiFi calling for SIM-only and postpaid customers, including eligible MVNOs on the Optus network.
• TPG / Vodafone supports WiFi calling for subscribers on the TPG network.

This means that the majority of Australian mobile users — regardless of which of the three major networks they are on — have WiFi calling available to them at no additional charge. Most residential and business mobile plans include unlimited national calls, so WiFi calls are billed identically to standard mobile calls under existing plan inclusions.

Device Support

WiFi calling is supported natively by:

• All Apple iPhone models from iPhone 6 onward running a current version of iOS
• Samsung Galaxy S series from the S7 onward and A series from the A30 onward
• Google Pixel phones (all current models)
• The majority of modern Android smartphones from major manufacturers including Oppo, Motorola, and Sony

Older or budget handsets may not support WiFi calling, and some carrier-specific firmware requirements apply for certain Android models on the Optus network. For any building-wide deployment, it is reasonable to assume that the majority of modern devices carried by tenants and staff will be WiFi calling-capable.

How WiFi Calling Works in a Commercial Building

The mechanism is straightforward. When a smartphone connected to a WiFi network detects that the cellular signal has dropped below a usable level (typically around -100 dBm RSSI or worse), it automatically routes any outgoing or incoming voice calls through the WiFi connection instead. The call is transmitted as encrypted data packets across the internet to the carrier's core network, where it is bridged back onto the public switched telephone network (PSTN) and delivered as a normal call.

From the building's infrastructure perspective, a WiFi call is a stream of UDP packets traversing the network to the carrier's VoWiFi gateway. The session is encrypted end-to-end using IPsec, which means the building's internet connection cannot inspect or intercept the call content — only carry the traffic.

What the Building Needs to Provide

Three conditions must be met for WiFi calling to work reliably throughout a commercial building:

1. A building-wide managed WiFi network with consistent coverage. The WiFi signal must reach every area where cellular coverage fails — basements, car parks, lift lobbies, plant rooms, and interior office spaces. Consumer-grade routers cannot achieve this in a multi-storey commercial building. Enterprise access points, correctly placed, cabled, and configured, are required.

2. Device compatibility. The tenant's smartphone must support WiFi calling. As noted above, all modern iOS and Android devices do. Older or entry-level handsets may not.

3. Carrier enablement. The tenant's carrier must support WiFi calling. All three major Australian carriers do.

When all three conditions are met, WiFi calling is automatic and transparent. There is no configuration required on the tenant's part beyond ensuring WiFi calling is enabled in their device settings — a feature that is on by default on most modern handsets.

Why Building WiFi Must Be Managed, Not Consumer-Grade

This is the element that building managers most commonly underestimate. WiFi calling places specific demands on the network that a consumer router — or a collection of independently configured access points without centralised management — will not reliably meet.

The Problem with Consumer and Unmanaged WiFi

A domestic WiFi router is designed to serve a small number of devices in a single room or small apartment. When deployed in a commercial building, it creates:

• Coverage gaps between routers where signal strength falls below the threshold needed for a call to continue
• Roaming failures where a device moving through the building (in a corridor, on a lift lobby, in a stairwell) cannot transition smoothly between access points, causing the call to drop
• Interference from multiple uncoordinated access points broadcasting on the same or overlapping channels
• No quality of service prioritisation, meaning a large file upload by one user can degrade the latency of every WiFi call on the network simultaneously

What a Managed Enterprise WiFi Network Provides

For WiFi calling to work reliably as a substitute for cellular coverage, the building's WiFi network must meet the following technical standards:

Seamless roaming (802.11r). IEEE 802.11r — also known as Fast BSS Transition — allows a device to pre-authenticate with the next access point before it disconnects from the current one. This reduces the handoff time between access points from hundreds of milliseconds to approximately 40–50 milliseconds. Without 802.11r, a person walking from the car park to the lift lobby while on a call will experience a brief interruption as the device roams; with 802.11r correctly configured, the transition is imperceptible.

Adequate signal strength throughout the coverage area. The minimum signal strength threshold for reliable voice traffic over WiFi is -67 dBm RSSI. Below this threshold, packet loss and latency increase to levels that produce audible call degradation. Access point placement must be planned to maintain -67 dBm or better in every area where coverage is intended — including the corners of car parks, inside lift lobbies, and in plant rooms.

Low and consistent latency. WiFi calling is sensitive to latency spikes. Industry guidance recommends that one-way latency not exceed 150 milliseconds for acceptable voice quality. A managed network with QoS policies configured to prioritise UDP voice traffic over bulk data transfers maintains the latency envelope that VoWiFi requires.

Quality of Service (QoS) configuration. Without QoS, a tenant downloading a large file or running a software update can consume available bandwidth and introduce jitter that degrades every active voice call on the network. Enterprise WiFi platforms allow voice traffic — identified by its DSCP marking — to be queued ahead of non-real-time traffic, ensuring that call quality is maintained even under load.

Adequate backhaul and internet capacity. Each active WiFi call consumes approximately 64–128 kbps of internet bandwidth (depending on the codec used by the carrier). For a building with significant tenant density, the internet connection must be sized to carry simultaneous calls without bandwidth contention. This is generally not a large capacity requirement — even 30 simultaneous calls consume less than 4 Mbps — but it must be factored into the internet service plan.

For more on how building network design affects both security and coverage, and on the specific considerations for managed WiFi for buildings, the supporting articles in this series cover those topics in detail.

The Alternative: Distributed Antenna Systems

Before WiFi calling became practical, the standard solution for in-building mobile coverage was a Distributed Antenna System (DAS). It remains the right solution in specific contexts, but it is not the right solution for most commercial buildings and apartment complexes.

How DAS Works

A DAS installation uses a network of small antennas distributed throughout a building to rebroadcast the carrier's own cellular signal. A passive DAS uses coaxial cable splits to distribute signal from a donor antenna mounted on the roof. An active DAS uses powered signal amplifiers and fibre or coaxial distribution to extend the carrier's signal to every floor and room in the building.

Both approaches provide genuine cellular coverage — the device is connected to the carrier's network as if it were outdoors, and WiFi is not involved at all.

Why DAS Is Not the Right Answer for Most Buildings

The cost and complexity of a commercial-scale DAS installation is prohibitive for the majority of building types. Active DAS systems for multi-carrier coverage in a commercial building cost between AUD $2 and $10 per square foot depending on the number of carriers and the complexity of the installation — and often significantly more in Australia once compliance costs and carrier coordination requirements are included.

For a 5,000 square metre commercial building, this translates to a DAS investment that can exceed $500,000 before carrier agreements are in place. Carrier coordination — required because the DAS is rebroadcasting the carrier's licensed spectrum — adds months to the project timeline and requires separate agreements with each carrier whose signal is to be distributed.

DAS is the appropriate solution for large hospitals, stadiums, convention centres, major transport hubs, and other venues where thousands of simultaneous users require native cellular connectivity and WiFi is impractical. For a commercial office building, a residential apartment complex, or a mixed-use development, managed WiFi with WiFi calling delivers equivalent day-to-day call quality at a fraction of the cost.

Direct Comparison: WiFi Calling vs DAS

Emergency Calls (000) and WiFi Calling

This is a question every building manager should ask before relying on WiFi calling as the primary connectivity solution for any part of the building. The answer is reassuring, but it requires verification.

All major Australian carrier implementations of WiFi calling are required to support Triple Zero (000) calls. When a device makes a 000 call over WiFi calling, the call is routed through the carrier's VoWiFi gateway and bridged to the Emergency Call Service in the same manner as a standard 4G VoLTE call. The ACMA's Telecommunications (Emergency Call Service) Amendment Determination 2024 strengthened obligations on carriers to maintain 000 access through non-cellular pathways following the 3G network shutdown.

However, building managers should verify two specific points:

1. Lift and emergency area coverage. The requirement that lifts and emergency areas have working communication is separate from WiFi calling, and is governed under relevant state-based building codes and the BCA. Lifts in Australia require compliant emergency telephones — dedicated hardwired devices that do not depend on mobile or WiFi networks. WiFi calling does not satisfy this requirement, and should not be treated as a substitute for lift emergency phone compliance. WiFi calling coverage in lift lobbies, however, does improve the ability of building occupants to call for help from mobile devices before entering a lift.

2. Connectivity continuity. A WiFi calling-dependent 000 call relies on the building's internet connection remaining active. If the internet service is down — due to an ISP outage, a power failure without UPS, or a network equipment failure — WiFi calling is unavailable. Buildings with life-safety requirements should assess whether redundant internet connectivity or cellular backup is warranted.

For most commercial tenancies and apartment buildings, WiFi calling provides a material improvement in emergency communication capability in dead zones, because it gives occupants connectivity where they previously had none. It should be implemented alongside, not instead of, hardwired emergency communication systems in required areas.

Tenant Benefits and the Commercial Leasing Case

The practical improvements for building occupants are immediate and tangible:

• No dropped calls in car parks. A tenant who previously had to stay on the open-air ramp to finish a call before entering the basement can now take calls throughout the car park.
• Continuous calls in lifts. With WiFi coverage extending to lift lobbies and, where cabling permits, lift cars, conversations are not interrupted by elevator travel.
• Improved data speeds in signal-poor areas. WiFi calling operates over the same WiFi network that provides internet access. In areas where cellular data was previously unavailable, tenants also gain WiFi data connectivity.
• No change in call appearance. Calls made and received over WiFi calling display the caller's normal mobile number. There is no additional number, no VoIP app, and no change to the way calls are billed under the tenant's mobile plan.

In commercial leasing, building amenity increasingly includes connectivity. Tenants evaluating office space now routinely assess mobile coverage alongside other infrastructure factors. A building with documented, building-wide mobile coverage via a managed WiFi network is a more attractive proposition than one where tenants must walk to the window to make a call.

For strata committees managing residential apartment complexes, WiFi calling coverage in car parks and common areas directly reduces the volume of complaints about mobile connectivity — one of the most common maintenance grievances in buildings with below-grade car parking.

For more background on the full scope of mobile dead zones in buildings and the range of available solutions, that resource covers the problem in detail.

Planning a Building WiFi Calling Deployment

Deploying a managed WiFi network capable of supporting WiFi calling requires structured planning across four areas: coverage design, physical infrastructure, network capacity, and ongoing management.

Coverage Design

The starting point is a coverage survey — either a physical RF survey of the building using a spectrum analyser or a predictive model built from the building's floor plans and materials data. The survey identifies the locations where cellular signal is absent or insufficient, and the access point placement required to deliver -67 dBm or better throughout those areas.

Specific attention is required for:

• Basement car parks: Large open spaces with concrete columns. Access points must be ceiling-mounted with coverage designed to eliminate shadows between columns and around concrete cores.
• Plant rooms and comms rooms: Dense metal equipment and enclosed construction require access points positioned inside or immediately adjacent to the space.
• Lift lobbies: Access points placed to cover the lobby area on each floor, providing connectivity as tenants wait for and exit lifts.
• Interior floor areas: For deep-floorplate buildings, access point density must be sufficient to cover the building core without relying on signal from exterior-facing access points.

Physical Infrastructure: Cabling and Power

Every enterprise access point requires a dedicated Ethernet cable run from the access point location back to a network switch, and power delivered over that cable via Power over Ethernet (PoE). This is distinct from any wireless mesh approach — mesh systems introduce additional latency and throughput loss that is incompatible with reliable voice performance.

The physical cabling infrastructure must be planned before construction or fit-out wherever possible, as retrospective cabling in a completed building is significantly more expensive. For new developments and major refurbishments, WiFi coverage design should be incorporated into the services engineering scope at the design stage.

The access point cabling requirements for building-wide WiFi are covered in detail in the structured cabling guide.

PoE Switch Capacity

The network switches that power the access points must have adequate PoE budgets for the number and type of access points connected. Enterprise access points typically draw between 15 and 30 watts per unit. A building with 20 access points will require switch PoE capacity of 300–600 watts, which must be factored into the electrical and UPS design for the comms room.

Internet Connection Sizing

As noted earlier, each active WiFi call consumes 64–128 kbps. This is not a large bandwidth requirement per call, but the internet connection must also carry all other building traffic — tenant internet access, building management systems, IP security cameras, and any hosted services. A fibre internet connection sized for the building's total traffic load with headroom for growth is the appropriate starting point. A dedicated QoS policy on the WAN interface ensures that voice traffic is prioritised at the network edge.

Frequently Asked Questions

Q: Does WiFi calling work automatically, or do tenants need to configure anything?

A: WiFi calling is enabled by default on most modern iPhones and Android phones. Tenants generally do not need to change any settings — the feature activates automatically when the device detects insufficient cellular signal and a WiFi network is available. Some devices require the feature to be turned on in settings if it was previously disabled. Building managers should communicate to tenants that the building WiFi network supports WiFi calling and encourage them to verify the setting is active on their devices.

Q: Will WiFi calling work on all three major Australian networks — Telstra, Optus, and TPG/Vodafone?

A: Yes. Telstra, Optus, and TPG all support WiFi calling for their subscribers and for eligible customers on their MVNO networks. The building WiFi network carries the data packets regardless of which carrier the tenant is on. There is no network-side configuration required to support multiple carriers — WiFi calling is managed entirely between the device and the carrier's servers via the internet.

Q: What happens to a WiFi call if the internet connection drops briefly?

A: A brief internet interruption — under approximately two seconds — will typically cause the call to drop. Unlike a browser session, which can resume seamlessly after a connection hiccup, a voice call is a real-time session with a strict latency requirement. This is a reason to ensure the building's internet connection is provided on a reliable, business-grade service rather than a residential plan, and to consider whether a secondary connection or 4G failover is appropriate for the building's risk profile.

Q: Can WiFi calling replace the need for a DAS in any building?

A: For most commercial office buildings and residential apartment complexes, yes — WiFi calling over a well-designed managed WiFi network delivers equivalent call quality to a DAS at substantially lower cost. The exception is venues where very high densities of simultaneous users require native cellular capacity (stadiums, large hospitals, major transport interchanges), or where all devices must be supported regardless of age or WiFi calling capability. For those scenarios, DAS remains the appropriate solution.

Q: Does the building WiFi need to be on a separate network from tenant internet access for WiFi calling to work?

A: Separation is not required for WiFi calling to function, but it is recommended for security and network management reasons. A well-managed building network typically uses VLANs to separate building common-area WiFi from tenant networks, with QoS policies applied at the VLAN level to ensure voice traffic is prioritised correctly. This also prevents traffic from one tenant's network affecting call quality experienced by other tenants or common-area users.

Get WiFi Calling Coverage Throughout Your Building

Pickle designs and manages enterprise WiFi networks for commercial buildings, apartment complexes, and mixed-use developments across Australia. Our deployments cover the areas standard networks miss — basements, car parks, plant rooms, and lift lobbies — using enterprise-grade access points, structured cabling, and managed network infrastructure configured specifically for voice traffic performance.

If your building has mobile dead zones that are frustrating tenants or affecting your leasing proposition, the solution is a managed WiFi network designed for the job.

Call us on 1300 688 588 or email [email protected] to discuss a coverage assessment for your building.