The Australian Federal Court has granted an injunction preventing Telstra from continuing its "unlimited" mobile advertisements, after finding they constitute misleading and deceptive conduct.

According to Justice Gleeson, Telstra's advertisements "falsely convey the representation" that the telco offers a mobile product with no limits on data speeds, data volumes, and the ability to download data without interruption or delay, misleading the public on the nature and characteristics of mobile products including the geographical reach of its network.

This is in contravention of both Australian Consumer Law and the Competition and Consumer Act, Gleeson J said.

In arguing for injunctive relief to be imposed as soon as possible, counsel for Optus pointed out that Telstra's street furniture campaign has already run its course, while it could take up to three days for Google to take down the online Google Search advertising.

The judgment should also apply to all ads that are "substantially similar", counsel for Optus said, adding that the court should ask Google to take down all advertising on Wednesday.

Optus also flagged that it is seeking monetary relief and permanent injunctive orders to be decided in a case management hearing on June 1, with Telstra on Wednesday also ordered to pay Optus' legal costs.

The decision had been delayed by an hour on Wednesday morning due to "IT issues" impacting Justice Gleeson's ability to deliver the judgment.

During the hearing last week, Telstra's billboard and online ads that state, "One word from Australia's best mobile network: Unlimited" had come under fire.

Optus counsel Richard Lancaster SC had argued that Telstra's usage of the word "unlimited" is misleading, because ordinary consumers would be likely to think unlimited applies to characteristics across data speed, data volume, geographical reach, and availability across devices.

"Unlimited is a powerful word," Lancaster said, adding that Telstra's ads cause "a misleading impression intentionally created to draw consumers into the marketing web" and are "misleading and false".

"Its lack of specificity is in fact a huge part of the problem, because it invites consumers to think about what is important to them about a mobile network ... and telling them those are unlimited."

Speaking from her personal reaction to the word "unlimited", Justice Gleeson said she immediately inferred that it meant an unlimited network geographically with an absence of blackspots. Her second impression was that it would enable customers to stream videos wherever they go without issue.

Dispelling these impressions would require effort from the consumer to travel to a Telstra store and speak to an employee, Gleeson J pointed out, which she said could "pique fury".

"The idea that someone will then go and explore this through the internet is not such an imposition on the consumer; what I find more troubling is that someone would schlep to a Telstra shop to find out ... that in fact there was nothing relevant for them," Gleeson J said.

Throttling speeds after using the initial 40GB of data each month also leads to "usage that makes you miserable", the judge said, questioning whether Telstra wants "miserable customers".

Counsel for Telstra argued that the ads are not misleading because a reasonable reading of them would not expect the word "unlimited" to be applied to every single feature of every single product on offer from the telco.

"The way in which the ad is structured, it doesn't say, 'One word about Telstra's mobile network'. It says, 'One word from Australia's best mobile network'. It could just as easily be saying, 'One word from Telstra'. The impression that that sets up is this is the person who's speaking," counsel for Telstra said.

"Telstra's saying, 'One word from us, which is unlimited'. They're not saying, 'Here's a description of every single feature of every single product or service that we might offer'."

The ads simply prompt the consumer "to obtain additional information", he added, by piquing interest or curiosity to find out what is unlimited.

"The field of telecommunications is absolutely awash with unlimited advertising, and all that's happening is into that space has stepped Telstra to say, 'Here's a word from us: Unlimited. Come and find out more'," counsel for Telstra said.

"Our case is that it's an unreasonable and strained interpretation to use the word 'from' and turn it into an 'about'. That word standing alone, together with a prompt to say, 'If you want to find out more you can either visit us today, or if you're online and seeing things on social media you can learn more just by clicking, or you can go to the Telstra website again just by clicking'.

"To say that an ad in that form is describing every characteristic of every product and service on offer from Telstra we say is strained, and of the sort of reaction that should be excluded from the reasonable potential customer."

In another proceedings, Telstra last week obtained an interlocutory injunction from the Supreme Court of Victoria to prevent Optus from continuing to run ads claiming it has the best mobile network in Australia.

Optus was required to "take all necessary steps to withdraw any advertisements or promotional material containing the alleged representation", after Justice Robson found the ads may be misleading or deceptive.

"I am satisfied that there is a serious question to be tried in relation to the allegations of misleading or deceptive conduct on the part of Optus," Robson J said.

Optus' online ads and billboards across New South Wales, Victoria, and Queensland had used slogans such as "Empires end. That's what they do", and "The Optus Mobile Network has been ranked the best overall in voice and data", referring to last year's P3 Mobile Benchmark report, which saw Optus defeat Telstra by three points.

An Optus spokesperson responded by saying the P3 benchmark test "is worth celebrating and communicating", adding that Telstra has "lost its sense of humour". It has since changed its online advertising to read, "Australia's winning mobile network".

In a Q3 financial update earlier this week, Telstra said it expects its full-year FY18 earnings before interest, tax, depreciation, and amortisation (EBITDA) to be at the bottom of the AU$10.1 billion to AU$10.6 billion guidance range, and income to be around the middle of the AU$27.6 billion to AU$29.5 billion range.

On Thursday, Optus reported total net profit of AU$817 million for FY18, with EBITDA of AU$2.8 billion. During the year, Optus brought in operating revenues of AU$8.7 billion. Optus also announced reaching 10.1 million mobile customers.

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