One IT manager, who requested anonymity, told Computerworld the organization's phones went off at about 12.25pm Monday local time and was not restored until about 9pm, almost nine hours later.

"The latest information from Optus is that the problem was in the Blacktown [Sydney's west] exchange and that we are not the only Optus customer affected by this outage," the IT manager said. "[Optus] mentioned about a dozen customers when I was speaking to them last night."

The problem resulted in an inability for the companies to make outbound calls.While Optus is yet to notify customers of the exact nature of the problem, the IT manager said the company had "verbally" stated it resulted from the failure of a PSAX e1 connector.

"I have requested a written report to be forwarded to me [but Optus] is still not able to give me an ETA," the IT manager said.

Optus is yet to confirm the extent of the failure and which equipment may have caused it, but the company is known to use infrastructure from Lucent and Juniper.