Key takeaways
- Most services connected to the nbn won't work during a power outage, including calls to 000 from those phones.
- Every powered device in the call path needs backup power: the nbn connection box, router, switch and phones.
- A cloud phone system can keep calls flowing to staff mobiles through an app when the office is dark.
- Always keep a charged mobile phone available for emergency calls.
Why phones stop in a blackout
On the old copper network, a corded phone drew its power from the line. On the nbn, phones depend on powered equipment at your premises. The ACMA advises that most services connected to the nbn won't work during a power outage, which means you won't be able to call 000 from them.
nbn notes that each mains-powered device connected to the network needs its own battery backup, and that battery backups only last so long.
Map your call path
List every device a call passes through:
- the nbn connection box
- your modem or router
- network switches, which often power desk phones via Power over Ethernet
- any on-site phone system
- desk phones and cordless bases.
Backing up one device doesn't help if the next one in the chain goes dark.
Use a UPS where it counts
An uninterruptible power supply (UPS) keeps equipment running through short outages and gives servers time to shut down cleanly. Size it for the devices above, test it, and replace batteries on schedule. Backup power with automated shutdown is one of the protection layers we install for medical and business clients.
Let the cloud carry your calls
With a cloud phone system such as 3CX hosted in Australia, the phone system itself isn't in your building. If the office loses power or internet, calls can still ring on staff mobiles through the free softphone app, or divert to another site.
Check that diversion happens in the cloud or at the provider, not on equipment in your office that will also be off.
Plan for Triple Zero
Keep at least one charged mobile phone available at all times, and make sure staff know to use it for emergency calls during an outage. If you have medical alarms, lift phones or monitored alarms, ask the equipment supplier how they behave in a power outage.
Outage checklist
- Call path mapped, device by device
- UPS on the nbn box, router and PoE switch
- UPS tested in the last six months
- Softphone app installed for key staff
- Outage call routing set up in the cloud
- A charged mobile available for 000
- Staff know the outage plan
Common questions
Will my VoIP phones work in a blackout?
Not unless every device in the call path has backup power and your internet connection stays up. A cloud phone system can route calls to mobiles instead.
Can I call 000 from a VoIP phone?
You can call 000 from certain VoIP services, but most nbn services won't work during a power outage. Keep a charged mobile for emergencies.
How long does a UPS last?
It depends on the UPS capacity and how much equipment it powers. Size it for the devices you need to keep running, and test it regularly.
Reviewed by Graham Graieg and Dane, Triad Networking Services. Graham and Dane look after IT, phones and security for Triad's medical and business clients across South East Queensland. Meet the team.
Sources
General information only, current as of 6 October 2026. It isn't legal or compliance advice for your specific situation.