"After three weeks I said, 'Ziggy what is it like – is it like being back at Telstra'?" Mr Turnbull recalled. "He said 'no, it's worse than that – it's like being at Telecom.'

"Then he thought for a minute and said 'no, it's actually more like the PMG [Postmaster-General's Department]' and that is not an exaggeration."

The minister said that while things were getting better with the project back on track, the company still had big risks that could blow out costs and timings.

One of these was the rise of customers using wireless technologies to get high-speed broadband instead of fixed-line connections being built by NBN.

"That term 'future-proofing' is just nonsense and I wish we could just throw it out," he said. "A, you can't proof yourself against the future and B you shouldn't want to – you should embrace the future and embrace the volatility and put yourself and your firm, your government in an agile posture that enables you to make that volatility your friend and take advantage of it."

But despite saying in 2014 that the NBN could de-risk by getting Telstra to help build the project, Mr Turnbull told the conference he was relaxed about the news that Telstra had chosen to walk away from the construction tender.

"Telstra is very involved with the design, what they're not participating in is the actual construction and delivery," he said. "That's their call … but we have a very good relationship with Telstra and it's not antagonistic.

"There are other things I'm more anxious about than that bit."

NBN chief executive Bill Morrow told ABC radio on Thursday morning that price terms may have been the reason for Telstra's departure.

"When we looked at the market rates, trying to get the best value for the taxpayers, Telstra felt that was something that they didn't want to participate in any further and they pulled out," Mr Morrow said.