In this guide · 8 sections
Short answer
Add a dual-WAN router with a 4G or 5G SIM from a different telco than your fibre provider, so the office switches over automatically when fibre fails. Then check your POS and card terminals have their own fallback, turn on offline modes in key apps and test the failover every quarter.
What the March 2026 Singtel outage showed businesses
According to the Ministry of Digital Development and Information's reply to parliamentary questions, Singtel had difficulties with its mobile network between 16 and 18 March 2026. The 16 March incident affected more than 600,000 mobile customers and lasted about nine hours, attributed to a mechanical fault at a network facility. A separate incident on 17 March affected about 2,000 customers, caused by a software bug from a planned update. IMDA is investigating and has found no evidence of a cyber-attack.
News coverage, such as this Straits Times report carried by The Star, described disruption to payments, ride-hailing and food delivery. For small businesses the lessons are practical:
- A mobile hotspot from a staff phone is not a backup if the phone is on the network that failed.
- Card terminals, QR payments and delivery tablets often use mobile data, not your office line.
- Having two connections only helps if they do not depend on the same telco.
How a 4G or 5G backup connection works
The usual set-up is a dual-WAN router: one port connects to your fibre router or ONT, and a second connection uses a mobile SIM, either built into the router or through a separate 4G/5G modem. When the router detects the fibre link is down, it moves traffic to the mobile connection, then switches back when fibre returns.
Router with built-in 4G/5G
Simplest- One box, one SIM slot or two
- Automatic failover
- Place it where mobile signal is good
Best for: Small offices and shops with one fibre line.
Existing router plus 4G/5G modem
Keeps current kit- Works if your router supports dual-WAN or USB modems
- Modem can sit near a window for signal
- One more device to power and maintain
Best for: Offices that already have a business-grade router.
If you are setting up or upgrading the network anyway, our office network and Wi-Fi guide covers routers, switches and access points.
Setting up the backup, step by step
Pick a different telco for the backup SIM
If your fibre is from one provider, take the mobile data SIM from another. Check which network most staff phones use and avoid that too if you can.
Check signal where the router will sit
Run a speed test on a phone using the chosen network at the router's location. Basement and interior rooms can have weak signal; a window position or external antenna helps.
Choose a data plan sized for outages
Estimate a working day of email, cloud apps and video calls. A plan with enough data for a few full days is usually sufficient for a backup line.
Configure failover and priority
Set fibre as primary and mobile as backup, with health checks against a reliable address. Optionally limit large updates and backups on the mobile link.
Connect critical devices to the router
Make sure POS, phones (if VoIP) and key PCs run through this router, not through a separate ISP box that will not fail over.
Power it properly
Put the router, ONT and switch on a small UPS so a brief power cut does not take down both connections.
Keep payments and POS working
Payments are usually what hurts most during an outage. Each device may connect differently, so check them one by one.
| Device or service | How it usually connects | What to check |
|---|---|---|
| Card terminal | Office Wi-Fi, Ethernet or its own SIM | Which network its SIM uses; whether it can switch to Wi-Fi from the backup router |
| Cloud POS on a tablet | Office Wi-Fi | Whether it has an offline mode and how it syncs sales later |
| PayNow or SGQR at the counter | Customer's phone | Works if the customer has signal; your confirmation device needs a connection |
| Delivery platform tablets | Wi-Fi or SIM | Put them on the backup router or a SIM on another network |
Offline modes differ widely: some POS systems queue card payments and sync later, others cannot take cards offline at all. Our POS system comparison is a starting point; ask your provider directly what happens without a connection.
Cloud tools: what still works offline
Most cloud apps need a connection, but some keep working for a while if you prepare in advance.
Prepare these before an outage
These steps fit into a wider continuity plan. Our IT business continuity plan template covers who decides, who calls the ISP and how to tell customers.
Test the failover every quarter
A backup line that has never been tested often fails on the day: the SIM has expired, the plan ran out or the router settings were reset.
A good quarterly test
- Unplug the fibre during a quiet hour
- Check email, POS and a video call work
- Time how long the switch takes
- Plug fibre back in and confirm it switches back
Common reasons the backup fails
- Prepaid SIM expired or out of data
- Router firmware reset removed failover settings
- Card terminal still on the old ISP box
- Router placed where mobile signal is weak
Do it yourself or get help?
If you already have a router that supports dual-WAN, adding a backup SIM and failover is a manageable DIY job with the router's manual. Getting POS, terminals and VoIP phones all onto the right network takes more checking.
Our Quick Fix (1 hour) (S$119) covers one well-defined remote task, such as configuring failover on a supported router or checking which devices bypass it. If it needs longer, we quote before continuing. We work remotely, so hardware installation on site is not included.
Frequently asked questions
For most small offices, a dual-WAN router with a 4G or 5G data SIM from a different telco than the fibre line is the simplest reliable option. It switches over automatically, needs little maintenance and covers both fibre faults and single-telco outages. A second fibre line is an option for larger offices.
Yes. If your fibre and backup SIM are from the same provider, a problem in that provider's network can take out both. The March 2026 Singtel mobile outage, which MDDI says affected over 600,000 customers, showed that a single network can fail for hours. Spread connections across providers.
It depends on how it connects. Some terminals have their own SIM and keep working if their mobile network is up; others use office Wi-Fi or Ethernet. Some POS systems can queue payments offline, others cannot. Check each device and ask your payment provider about offline behaviour before an outage.
It depends on your work. Email and cloud apps use relatively little; video calls and large file syncs use much more. Estimate a normal day's usage from your router or ISP portal, then pick a plan that covers a few days. Pause large backups and updates on the mobile link to save data.
For one or two people briefly, yes, but it is not a business backup. A hotspot cannot connect card terminals, POS tablets and desk phones easily, it drains the phone, and it fails if the phone is on the same network that is down. Use it as a last resort.