Bushfires have been the biggest natural disaster to hit Telstra's infrastructure.
Regional General Manager for Southern NSW, Chris Taylor, said the height of the bushfires between New Year's Eve and Saturday, January 4, caused outages along the South Coast.
On Monday, January 13, Mr Taylor told Australian Community Media that 12 mobile tower sites on the South Coast had been impacted and five destroyed.
The bushfires were the "biggest scale of event" the company has dealt with.
He said the South Coast had more than 40 mobile base stations off the air, mostly due to power outages.
"It was primarily due to the mains power across the region being impacted," Mr Taylor said.
Once mains power is lost, mobile towers switch to battery reserves. He said there were multiple cases where the reserves had "run out".
At Narooma, Mr Taylor said towers were off the air for up to five days due to power outages.
He said Lake Conjola was an area completely isolated on New Year's Eve with no power or telecommunications. It was restored after 10 days.
"We were able to restore fixed lines and mobile services there last Friday, which was a priority," Mr Taylor said.
It was a long wait for the area to be declared safe to access.
"It took a long time to get clearance," he said.
After the bushfire ravaged the coast on New Year's Eve, Mr Taylor said Telstra was in "response mode".
"We have been trying to get things back up and working for emergency services and to have connectivity for people in these communities," he said.
"Now things have settled this week, we are in recovery mode.
"We are assessing our network and the impacts of the fire, working on restoration and rehabilitation."
At bigger towns, he said the network was not completely lost. There were multiple mobile towers to pick up the slack of those damaged.
"It lessened and reduced the capacity but it still held on," he said.
Mr Taylor said the tower at Surf Beach was completely destroyed and Malua Bay's was badly fire damaged.
He said the Mount Wandera tower was "pretty much destroyed" and crews were finding it difficult to gain access in the rough country.
"The Defence Force had removed trees at the Wandera site, allowing us safe access," Mr Taylor said.
The most significantly damaged tower was that at East Lynne after the Currowan fire rolled through in November.
On average a mobile tower costs $1 million. Mr Taylor said repairs will take "weeks and months".
"When it's safe to go into areas, we will inspect the network and identify any damaged cables so we can build a view of what we need to replace," he said.
"Significant work needs to be done to replace copper cables."
On Thursday, January 9, fixed services were restored at Malua Bay.
On Monday, January 13, crews were installing generators at the Nerriga tower, south-west of Nowra.
"Nerriga lost mobile coverage during the Saturday's (January 4) extreme conditions," Mr Taylor said.
"We were able to get access over the weekend and found there was no damage from the fire."
Information for farmers
Telstra is urging farmers to Dial Before They Dig, if they are planning to do any recovery work on their properties following recent bushfires.
Telstra's Regional General Manager Chris Taylor said lots of clean-up work is expected and while Telstra understood property owners were getting on with the job, any ground-breaking activity could damage the underground communications network and affect vital services.
"When our fibre optic cables are cut, there can be some really serious consequences for the region," he said.
"It can mean entire communities are disconnected, potentially preventing them from working, connecting with their family, and even calling Triple Zero (000), which in some instances can be life threatening.
"Whether it's replacing a damaged fence, burying livestock or even simply digging in your own back yard, you can sever our cables and take customers, including emergency services, offline.
Before undertaking a ground-breaking activity such as excavating, lodge an enquiry with Dial Before You Dig.
There are several ways you can contact Dial Before You Dig to lodge your request online, anytime at www.1100.com.au, download the 1100 Dial Before You Dig iPhone App or dial 1100 from your phone, anytime during business hours.