Most advice treats 5G as the backup that sits behind a proper line. For a growing number of businesses that has stopped being true, and the mobile connection is now the main one. It is not right everywhere, and the places it falls down are specific and predictable rather than vague. Here is an honest read of both.
The 30-second version
- 5G can genuinely be a primary business line, particularly where fibre has not arrived or the install is months away.
- Speed is rarely the problem. The things that catch people out are the public IP address and contention.
- No public IP on a standard plan means inbound VPNs, port forwarding and remote access to cameras will not work.
- Speeds vary through the day in a way a fixed line does not. Plan for the busy hour, not the quiet one.
- No guaranteed fix time. If downtime stops you trading, that is the argument for a leased line, not a faster SIM.
- Where it fits, it fits very well: live in days, movable, and no civils quote.
On this page
Where 5G works as a main line
The case for it is strongest in four situations, and in all of them the deciding factor is something other than raw speed.
- Fibre is not available or not soon. A quoted install of three or four months, or a civils charge running to thousands, changes the maths entirely. A 5G router is live the day it arrives.
- The premises are temporary. A site office, a pop up, a unit on a short lease. Nothing justifies a three year line.
- You cannot install cable. Listed buildings, leasehold units, landlords who will not grant a wayleave. We have written about what happens when a landlord sits in the middle.
- The business is small and mobile. A handful of users doing email, cloud applications and card payments does not need a dedicated circuit.
In those cases 5G is not a compromise. It is often the better engineering answer as well as the quicker one.
The public IP problem
This is the single most common reason a 5G main line fails for a business, and it has nothing to do with speed.
Standard mobile plans put you behind carrier grade NAT. You share a public address with many other customers and you do not get one of your own. Most things carry on working perfectly, because they start from inside your network. What stops working is anything that needs to be reached from outside.
| Still works | Does not work without a public IP |
|---|---|
| Browsing, email and cloud applications | Port forwarding to a server or recorder |
| Card payments and EPOS | Remote access to CCTV from outside |
| Hosted phone systems and video calls | A VPN that staff dial into |
| Cloud backup and file sync | Site to site VPN initiated towards you |
| Outbound remote support tools | Anything a supplier dials into |
The fix is a fixed IP or private APN SIM, which gives you an address of your own. It is worth deciding this before you order rather than discovering it when the alarm company cannot connect.
Contention and the busy hour
A fixed line gives you roughly the same speed at nine in the morning and nine at night. A mobile connection shares a cell with everyone else on it, so throughput moves through the day and with the weather and with whatever is happening nearby.
For most business use that variation is invisible. Where it shows up is the moment you are busiest, which is often when everyone else is too. If you are in a town centre at lunchtime, or near a venue on an event night, the connection you tested at eleven in the morning is not the connection you get.
Test at the wrong time deliberately. Before committing, run the connection at your busiest hour from the position the router will actually live in. That single test tells you more than any coverage map.
What you do not get
Being straight about this matters more than the sales case.
- No guaranteed fix time. Mobile networks do not offer the kind of service level a leased line carries. If a cell has a fault, you wait like everybody else.
- No uncontended bandwidth. You are sharing, by design.
- No symmetrical upload. Upload is better on 5G than 4G and still well short of a leased line.
- Coverage can change. A new building, new foliage or a mast change can alter what you get, and you have no say in it.
If an hour offline costs you serious money, that list is the argument for a leased line with a guaranteed fix time. Our post on what an hour offline actually costs is the honest way to work out which camp you are in.
Where Starlink fits
Satellite is worth considering in the same conversation, because it solves a slightly different problem. 5G needs a mast within reach. Starlink does not, which makes it the stronger option genuinely rural sites where mobile coverage is poor in every direction.
The trade-offs are similar in shape and different in detail: speeds vary, standard plans are also behind carrier grade NAT, and the equipment needs a clear view of the sky. We have written up the practical side in running Starlink behind a UniFi or Omada gateway.
As a rough rule: if you have usable mobile signal, 5G is simpler and cheaper. If you do not, Starlink is often the only thing that works.
How to decide
- Check what fixed options exist first, including the ones a single checker will not show. Being told fibre is unavailable is not the same as it being unavailable.
- List what has to be reachable from outside. Cameras, VPNs, anything a supplier dials into. If that list is not empty, budget for a fixed IP.
- Test at your busiest hour, from where the router will live, not from the car park.
- Price the downtime. If an outage is an inconvenience, 5G is fine. If it stops you trading, you want a line with a fix time, or 5G plus a second path.
- Consider both. 5G as the main line with a second connection behind it is a legitimate and often cheap arrangement.
Not sure whether 5G would carry your site?
Give us the postcode and tell us what has to work. We will check real coverage, tell you which network suits the building, and say plainly whether a fixed line would serve you better. We would rather tell you that now than after the install.