"This will be part of the goodwill if the Optus acquisition deal goes through," a SingTel spokesperson said in an email response Tuesday.
Optus is in the process of being bought over by Singapore Telecoms Ltd in a deal said to be worth A$17 billion (US$8.4 billion) .
The Australian telco's write-off for One.Tel follows a similar move by Telstra Corp, Australia's largest phone company, which wrote off a A$36 million (US$18.6 million) One.Tel debt earlier this month.
According to a Reuters report, Optus said the amount would be written off against profit.
One.Tel, which was in the red for up to A$862 million (US$446.1 million), declared itself insolvent on May 30, and appointed outside administrators.
"Optus will try to recover this money from One.Tel," the country's second largest telco said in a statement. "However, statements by the administrators indicate creditors cannot be certain of recovering any money owed."