Australians are being urged to upgrade their mobile phones and check their medical devices as Telstra and Optus jointly announced the 3G network shutdown would be pushed back to October 28.
Both telcos had been preparing to switch off from the end of August but a recent Senate inquiry confirmed thousands of phones would not be able to make triple-zero calls after the shutdown.
The inquiry was also told critical medical equipment, personal cardiac alarms, EFTPOS machines and waste and water infrastructure could be cut off.
A joint statement from Telstra and Optus said the companies would undertake a mass public safety campaign to ensure users were aware they needed to upgrade.
The companies said it was critical customers check handsets are compatible with 4G and 5G and be aware if other devices relied on 3G.
A category of phones that will not connect to triple-zero on 4G has been a major concern.
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 might not realise their phone is configured this way by the manufacturer until the 3G network is switched off.
There were still 77,000 affected handsets in early August and Optus data revealed many users were international students or migrants.
All telcos have a service for customers to check the status of their device by texting "3" to the number 3498.
~ with AAP
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