An Optus advertisement showing a Telstra phone box sinking in the desert has been described as “humorous” and not misleading consumers in a court ruling after a legal battle between the rival telcos.

Australia’s biggest telecommunications company Telstra took Optus to court over the series of ads which included the tagline "Empires end. That's what they do" and referenced Optus' top ranking in the P3 Mobile Benchmark in December.

The ad was designed by Optus’ internal agency Yes Agency. The phone box did not show the Telstra logo, but Judge John Robson said earlier in the proceedings that its "distinctive shape, and blue-and-orange colour scheme" made it "easily recognisable as a Telstra phone box of the type that was once commonplace on Australian streets".

Telstra alleged the advertisement made it appear there had been a "significant and permanent change in the relationship between the Telstra and Optus mobile networks" and that Optus was "undisputedly" operating a better mobile network than Telstra.

But Mr Robson's judgment in the Supreme Court of Victoria on Wednesday found Telstra had failed to establish the Optus advertising was "misleading or deceptive”.