What is PTT over Cellular?

The idea in one sentence

PTT over Cellular — usually written PoC — turns a smartphone or a rugged handheld into a two-way radio that talks over mobile networks (4G, and where available 5G) and WiFi, instead of over its own private radio infrastructure. You press a button, you talk, and everyone in your group hears you instantly. What's different from traditional radio is what carries the call underneath: a mobile network you don't have to build or maintain.

If you've used a voice note on WhatsApp, you already understand half of it. PoC is that instant-voice idea, but built for work — a real push-to-talk button, live group calls, no waiting for a message to "send," and devices tough enough for a job site.

Why operations are moving to it

Traditional professional radio — LMR, or land mobile radio — needs its own network: repeaters on towers, antennas, frequency licences, and site infrastructure. That network gives you control and reliability, but it is expensive to build, and its coverage stops at the edge of where you've installed it.

PoC borrows coverage that already exists. Wherever there is a usable mobile signal, your radios work — across a depot, a city, a region, or even across a border. There are no towers to build and no repeater channel to licence.

This matters in an African context specifically, because the ground reality is a 4G-first one. Across the continent, mobile operators have invested heavily — close to US$120 billion over the past decade — to push 4G out as the workhorse layer, lifting its population coverage to roughly 78% by the end of 2024³. In the larger markets that figure is higher still: 4G now reaches around 85% of the population in Nigeria, 97% in Kenya, and over 99% in South Africa². 5G, by contrast, remains a small fraction of connections — about 1.2% across the continent — and is largely confined to major cities¹. The practical takeaway: for professional PoC today, 4G is what you build on — strong across cities and main routes, but genuinely thin or absent in remote areas. That gap is not a footnote; as you'll see, it's the whole reason the on-premises option exists.

The three things every PoC system needs

Every PoC setup, whatever the brand, is built from the same three parts. Understanding them makes every later decision clearer.

Users are the devices people carry. These can be ordinary smartphones running a PoC app (iOS or Android), or purpose-built rugged devices with a real PTT button, loud clear audio, noise cancellation, a dedicated emergency button, and accessories like remote speaker-microphones and headsets. You can mix both — office staff on phones, field crews on rugged handhelds. Dispatchers sit here too, working from a screen in a control room.

Server is the "brain" that connects everyone. It knows who belongs to which talk group, who may call whom, and it routes every press of the PTT button to the right people. Where this server lives — rented in the cloud, or a physical box on your own site — is the single biggest design choice in PoC, and the next section is devoted to it.

Network is the connection that carries the calls: public mobile networks (4G/5G), WiFi, or a private LTE network of your own. PoC is flexible here — it can use whatever connection is available and switch between them.

What it can do

A good PoC system does most of what professional radio does, and several things radio cannot:

• Group calls and one-to-one calls
• An emergency button that alerts everyone at once
• Voice — and on some systems video — encryption for sensitive work
• Live location and GPS tracking on a dispatcher map
• Lone-worker protection that raises an alarm if someone stops responding
• Job ticketing, so tasks can be sent and acknowledged
• Seamless roaming with no border — drive from one region or country to the next and stay connected, with no gap at the edge of a radio network

Exactly which of these you get depends on the system you choose — one of the things the needs analysis sorts out — but that is the menu.

The big decision: cloud or on-premises?

This is where most of the real thinking happens. The PoC server can live in two fundamentally different places, and the right choice depends entirely on your operation.

One thing to clear up first, because it's a common misunderstanding: where your server lives and which network carries your calls are two separate choices. Cloud or on-premises is about the server. Public mobile (4G/5G), private LTE or WiFi is about the connection. They mix freely — and in particular, an on-premises server can run perfectly well over the ordinary public mobile network. You don't need a private network to justify owning your server.

So on-prem spans a range. At one end, an on-prem server running over the public mobile network — wide coverage and familiar connectivity, but with the server (and your data) under your own roof rather than a provider's. In the middle, an on-prem server with its own private LTE or WiFi for areas the public network doesn't reach. At the far end, a fully sealed network with no outside access at all — maximum security and independence, the choice for mining and defence. The common thread isn't being cut off from the public network; it's that you own and control the server.

Cloud is renting reach. On-prem is owning control — over the same public network, or your own. Most operations are happy renting; those who need the server in their own hands run their own box.

A word on "mission critical" (MCPTT)

You may hear the term MCPTT — Mission Critical Push-to-Talk. This is a stricter, standards-based form of PoC, first published by the mobile-industry body 3GPP in 2016⁴, and built for police, ambulance and fire services, where a missed call can cost lives. What sets it apart is built into the network itself: priority and pre-emption (mission-critical traffic pushes ahead of ordinary users when the network is busy) and guaranteed quality of service under congestion⁵ — assurances that ordinary commercial PoC does not provide.

For most businesses, MCPTT is more than you need, and more than you'd want to pay for. The industry's own rule of thumb is clear: choose MCPTT when communications must survive congestion and emergencies — public safety, emergency response, defence; choose ordinary PoC when rapid, cost-efficient deployment matters most — logistics, private security, enterprise operations⁵. The needs analysis raises MCPTT only when it is genuinely relevant. One honest caveat the standard itself acknowledges: once users roam onto a foreign network you don't control, even mission-critical guarantees weaken — worth weighing if cross-border reliability is essential.

Is PoC right for you? The questions that decide it

When you work through the RadioSelect needs analysis, these are the things it's really asking — and now you'll know why each one matters:

• Security and ownership. Do you need to own the server yourself? On-prem can still run over the public network — or, if your site is isolated, on a private one. Or is a cloud subscription acceptable?
• Scale. How many users at launch, and how many in a few years?
• Connection. WiFi/broadband only, or do you also need to link to an existing radio (PMR) network?
• Call capacity. How many calls need to happen at once — private, group, and between PoC and radio users?
• Purpose. Is this for your own organisation, or will you resell the service to others?
• Budget. What upfront investment, and what ongoing monthly cost, are you comfortable with?

There are no wrong answers. These simply steer you toward cloud, on-prem, or a hybrid that connects PoC to radios you already own. That is exactly what the assessment is for.