There were known to be 300,000 3G Medical Alarms (PERS) devices used by seniors using home care and living in aged care, Independent Living Units and retirement villages. 

Telstra has announced it is delaying its 3G closure, due to close on 30 June, as there are hundreds of thousands of Australians who could be blocked from making emergency calls once the 20-year-old network has been switched off. 

The telco is postponing the closure until 31 August to give people more time to upgrade their handsets. 

"We've decided to extend [the deadline] by two months, mainly due to feedback from customers that some of them need more time to upgrade," Telstra networks executive Channa Seneviratne said.  

The latest figures reveal more than 200,000 Telstra customers are still using 3G-only mobile phones that will no longer work when the network is switched off, or a subset of older 4G phones that could also be caught out in the shutdown. 

This subset of 4G handsets is of greatest concern because they're configured to default to the 3G network for triple-0 calls, meaning owners may not realise until they're in an emergency. Emergency call systems are essential to seniors.  

Telstra, Optus which is due to shut down its 3G network in September, and TPG, which closed its network in December, is urging customers to upgrade their 3G-only devices to 4G or 5G. 

Telstra has launched a simple service that customers can use to determine whether their device will be affected: SMS 3 to 3498. 

Of the 80,000 customers who have used the instant handset compatibility checker, only 10% have been advised they need to upgrade their devices.  

Those who still need to upgrade their handset will soon hear a short voice message when making an outgoing call, reminding them to act. 

The 3G shutdown will mainly affect Australians living in rural and regional areas where phone and internet coverage is more limited.