Telstra and Optus began switching off the ageing network in October, coinciding with harvest and bushfire seasons and prompting safety concerns among farmers.
A majority of grain producers reported a reduction in the quality of their mobile service, GrainGrowers' rural affairs manager Sean Cole told a Senate inquiry in Canberra on Wednesday evening.
"This potentially has dire implications (for) farm worker safety and natural disaster response, particularly in relation to fire," Mr Cole said.
About 90 per cent of producers surveyed by the growers' organisation two weeks ago experienced reduced service or, in some cases, new black spots, he said.
A farming family in Charters Towers had reception on only 20 per cent of their vast Queensland property after the shut down, compared to 90 per cent before, National Farmers' Federation acting chief executive Charles Thomas said.
"Despite the gravity of the concerns that we're hearing from our members right across the country, rural Australians don't believe that reporting these issues to their provider will lead to solutions," Mr Thomas said.
"People don't want to be on hold for hours only to be told they need to purchase more equipment - or worse - that there is nothing to be done."
Charles Thomas said the National Farmers' Federation is getting member reports of new blackspots. (Mick Tsikas/AAP PHOTOS)
Some rural Australians relied on "fortuitous" coverage under 3G, which has been lost in many cases, the inquiry was told.
But Optus executive Harvey Wright said less than one per cent of customer complaints to the telco since September 2024 related to 3G.
"We're pretty confident that, actually, we haven't seen any reduction in coverage," Mr Wright said.
Telstra's 3G network used to cover 2.65 million square km across Australia, whereas 4G has been expanded to cover three million sq km, executive Justine Rowe said.
There was a speed improvement of 10 per cent nationally, 20 per cent in outer regional areas and 50 per cent in remote parts of the country, Ms Rowe said.
"By repurposing our old 3G spectrum, we've been able to expand capacity and improve speeds," she said.
Ms Rowe acknowledged individual experiences could vary and Telstra would only know of problems if their customers reported them.
She encouraged affected Telstra customers to call the new dedicated 3G hotline on 1800 990 853.
During question time earlier on Wednesday, Indi MP Helen Haines said some of her constituents in regional Victoria had reported connectivity issues and asked what the government would do to ensure no one was worse off.
Communications Minister Michelle Rowland said she was closely monitoring reports of poor coverage and had requested weekly updates from the telcos.Â
