Telco TPG (TPM) has been fined $400,000 for failing to provide access to emergency numbers for customers who had not paid bills.
Federal Court Justice Mordecai Bromberg found that TPG failed to give access to triple-zero and 112 on more than 190 occasions between March and September 2011.
He also found the company did not ensure that almost 6,000 lines had access to emergency numbers over that period.
A software upgrade at TPG in 2011 barred all outgoing calls, including to emergency numbers, made from suspended and inactive accounts.
The error was discovered when a woman was barred from calling an ambulance for her sick husband from her home phone in September 2011.
The man suffered a heart attack and because of poor mobile phone reception, his wife could not relay important details about his condition.
He died in hospital days later.
The Australian Communications and Media Authority found that 193 emergency calls from TPG had been barred, and that 5,979 suspended or inactive accounts did not have access to triple-zero during the period.
Justice Bromberg said while the error might have been inadvertent, TPG had not taken reasonable steps to avoid it happening.
"In 2011 TPG did not have any policy or process in place to ensure that its controlled networks maintained 000 connectivity for all customers," he said.
TPG seemed to have a "lax approach" to important regulations, Justice Bromberg said.
"TPG's failure could easily have led to the death of a person who might otherwise have been saved," he said.