Turnbull is an experienced Barrister, for him to use the words "outright lie" outside the protections of Parliamentary privilege means he firmly believes he is untouchable.
Ordinarily, all political promises are specifically exempt from the TPA, now ACL, provisions of "false or misleading statements". Part of this is because they are non-commercial in nature.
But making promises of a purely commercial nature about the provision of services to the public generally by a business enterprise, Government or not, seems to me to fall squarely under the provisions of the ACL and could be taken up by the ACCC, if they wished.
Especially of interest to the ACCC should be any material information deliberately withheld in the Coalition Broadband Plan, which is, in effect, a commercial prospectus looking to raise $29.5 billion dollars from the public. Specifically, the Plan/Prospectus is silent on the single largest commercial risk of the project: Telstra's co-operation. There is an unconvincing statement saying 'they'll give us access because in the media they've said the copper isn't work much', but there's the glaring omission of any Risk Plan.
If the Coalition Plan relies on agreements or understandings already, made but not disclosed, with major commercial partners, that again would be an interesting topic for the ACCC, possibly even the ASX.
Such actions would make for an interesting election campaign.
The other law that could apply is Defamation, claiming in the public media someone has told "an outright lie" is a very strong statement, definitely impugning the reputation of the person attacked.
My limited understanding of Defamation Law in most States now is that Truth is a defence, but a real expert would have a proper understanding of the complexities and nuances. This is a private matter between those who feel their reputations have been defamed by these repeated statements in the public media.
But in the way of the Law and Elections, a full case doesn't have to be heard for there to be an effect and outcome.
Could Turnbull be subject to a temporary injunction restraining him from commenting at all, especially disparaging, the current NBN? We'll see.