Bushfires have been the biggest natural disaster to hit Telstra's infrastructure.
On Monday, January 13, Regional General Manager for Southern NSW, Chris Taylor said 12 mobile tower sites on the South Coast had been impacted and five destroyed and 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.
"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.
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.
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.