"We continue to choose the best of breed for the applications that support our customer services," McDonald said. "Optus has in place a team for system administration who support a wide range of operating systems [including] Linux."

A spokesperson for HP denied the company's products or services are being phased out by Optus, stating the company remains one its "most important customers both in terms of hardware and services".

"We continue to enjoy a strong relationship across the business and look forward to this continuing in the future," the spokesperson said.

Linux vendor Red Hat declined to comment.