Latency, jitter and symmetry decide it, not speed

A phone call uses about 100 kbps. Every option here has a thousand times that. The spec sheets are selling you the one number that does not matter.

Cisco’s engineering targets for business voice have not changed in two decades: one-way latency under 150 ms, jitter under 30 ms, packet loss under 1%. A G.711 call needs roughly 80 kbps per direction including overhead. So a 30 Mbps line and a 300 Mbps line carry a call identically – until the line starts varying.

Jitter is the variation in packet arrival time, and it is what makes a call sound robotic or clipped. It comes from contention: other traffic fighting yours for the same medium. A dedicated strand of glass has almost none. A licensed point-to-point radio link has very little, because the operator engineered and reserved that spectrum for you. A 5G cell is shared with every user in its radius, and its behaviour at 17:00 is not its behaviour at 05:00.

Symmetry is the quiet second factor. Your outbound voice is upload traffic, and upload is where wireless products are weakest. Retail 100 Mbps fibre in SA is symmetric on nearly every network – Vumatel, Openserve and Octotel sell 100/100, Frogfoot 120/120. The mobile networks measured 11–32 Mbps average upload in Q2 2026, and Rain’s fixed 5G network showed a 9 Mbps median upload in its most recent published Ookla figures. Enough for calls, but it is the first thing that collapses when someone starts a cloud backup mid-morning.

Three ways into the same cloud PBX

All three connections end at the same place: your VoIP provider’s network. What differs is the first few kilometres, and that is where the milliseconds are made.

A quick definition, because the market blurs it: fixed wireless here means a wireless ISP delivering internet over a dedicated radio link – a small dish on your roof aligned to a high site, usually on licensed spectrum. That is a different product from 5G FWA, where a router on your windowsill joins the same mobile cell as every phone in the neighbourhood. A WISP running its own radio network holds both ECS and ECNS licences from ICASA; the distinction matters because a licensed operator controls its own capacity, while a 5G router takes what the cell has left.

The measured ladder matches the engineering. In MyBroadband’s Q1 2025 speed test analysis of 793,772 tests, the top ten fibre ISPs averaged 7.41 to 14.44 ms latency. The two predominantly fixed-wireless ISPs in the national top 20, Wirulink and Herotel, came in at 20.84 and 21.53 ms – behind fibre, comfortably ahead of the mobile networks. The Q2 2026 mobile measurements put network latency at 28 ms (Rain) to 41 ms (Cell C), with MTN, Telkom and Vodacom clustered at 29–31 ms. Every one of those numbers passes Cisco’s 150 ms voice ceiling. They do not pass it equally, and the gap is all headroom you will want on a congested afternoon.

Fibre vs fixed wireless vs 5G: the head-to-head table

Nine factors a buyer actually weighs, with the winner marked per row.

Score it honestly: fibre takes six rows, 5G two, fixed wireless one. But the fixed-wireless column is the one to re-read – second place in almost every row is exactly what you want from the line you buy when first place is not available at your address.

Where each connection wins

Match the line to the job, not to the advert.

Fibre: when calls make you money

A sales team, a support desk, a practice taking bookings by phone: these run on upload and consistency, and business fibre with an SLA (typically R400–R1,000 a month depending on speed) is the boring, correct answer. The install wait is the only real cost. Order it the day you sign the lease.

Fixed wireless: when the trench never arrived

Industrial parks on the urban edge, smaller towns, farms and lodges: this is where a licensed WISP link is not a compromise but the professional option. The measured latency sits a hop behind fibre, business links come with SLAs and symmetric profiles, and installation is an antenna alignment rather than a wayleave application. WISP coverage maps and fibre coverage maps disagree constantly – check both before assuming you are stuck with mobile broadband.

5G: when speed-to-live beats everything

A new office that opens Monday, a temporary site, a pop-up operation: 5G is online the day the router arrives, month-to-month, no technician. With 58% population coverage it is also the option most likely to exist at any given urban address. Just buy it knowing what it is: a shared cell with no SLA, best-effort speeds and the highest jitter risk of the three. For a two-person office making a handful of calls a day, that trade is fine. For twenty agents, it is not.

For the provider-level version of this comparison – Rain’s actual 2026 plans and prices against retail fibre – see our Rain 5G vs fibre head-to-head.

The setup that survives outages: primary plus failover

The three paths fail for different reasons. That is not a problem, it is the design opportunity.

A cut trench does not take down a radio tower; a congested cell does not slow a glass strand. A dual-WAN business router that holds two of these paths at once covers most single points of failure for a few hundred rand a month, and your cloud PBX will not notice the switch.

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