Fire alarms, EFTPOS machines and medical equipment could be disrupted when 3G shuts down, as the major telcos prepare for up to 150,000 phone users to be cut off.
A Senate inquiry has been hearing about the impacts of the ageing 3G mobile network's looming closure, with telcos committing to their shutdown deadlines from August 31.
Telstra and Optus have been ramping up information campaigns through social media, letters, text messages and calls encouraging customers to upgrade their devices.
The Royal Flying Doctor Service relies on 3G for telehealth appointments, security cameras and clinicians' duress alarms, its chief information officer Ryan Klose told the inquiry.
Insulin pumps and pacemakers are also supported by 3G technology that will have to be replaced, Mr Klose said.
"There are a lot of devices out there which are used for critical situations that simply will not be (noticed) until it's too late."
Telstra and Optus have provided thousands of free or subsidised handsets to disadvantaged customers.
Despite their efforts the telcos expect some users will not upgrade before the network closes.
When asked how many people will be worse off and lose access to triple-zero, banking and telehealth services, Optus executive Harvey Wright said it could be as many as 150,000.
"The migration experience we've had to date is that you have to do two things: create awareness and remove barriers for customers to act, but then also prepare for the fact that some will not," Mr Wright told the inquiry at parliament house in Canberra on Wednesday.
"It's just human nature."
Telstra executives could not provide a similar estimate, but anticipated there would be customers who would not upgrade before the closure.
Both telcos said they had back-up plans to help any customers cut off.
Business owners are only just becoming aware of the broader implications of the closure, Australian Chamber of Commerce and Industry small business director Jodie Trembath told the inquiry.
3G often supports payment terminals, routers, scanners, fleet vehicle tracking tools, water and waste infrastructure, and fire alarms.
"The recent communications from government and the telecommunications industry have focused on triple-zero services and the impact on handheld devices like mobile phones," Dr Trembath said.
"But the broader business impact has been overlooked."
The federal government and industry have been working to reduce the number of devices that are not compatible with 4G for emergency calls.
These devices - often bought overseas or second-hand - use 4G data for regular calls and texts, but bump triple-zero calls to 3G because they are not enabled with a technology called Voice over LTE.
Users may not realise their phone is configured this way by the manufacturer until 3G is gone.
Both telcos said the scale of the issue was not known until early in 2024, when there were an estimated 740,000 affected devices.
About 65,000 of those devices were still in use as of Friday, the telcos told the inquiry.
Phone users can check the status of their device by texting "3" to the number 3498.
