The ad states that Telstra covers 99.3 per cent and Optus 98.5 per cent. Photo: Paul Jones

Telecommunications giant Telstra says advertisements by rival SingTel Optus make the false and misleading claim that there is little difference between the companies' mobile networks.

Australia's number one mobile phone company has taken the country's number to court over an Optus ad that states, 'When it comes to to the percentage of Australians, there isn't much difference between the networks.' The ads feature a picture of Australia, stating Telstra covers 99.3 per cent and Optus 98.5 per cent.

Counsel for Telstra, Matt Collins SC, told the Victorian Supreme Court that the ad had been ''carefully crafted to convey the false impression'' that ''there are no longer any material or significant differences between the Telstra and Optus mobile networks."

In fact, Telstra's network covers more than 2.3 million square kilometres, or 28 per cent of the Australian landmass. Optus's network is about 43 per cent that size, Dr Collins said, at 1 million square kilometres.

''That is no trifle,'' he said on Wednesday. ''The additional coverage means that there are about 1.3 million square kilometres of Australia where ... you are able to get a Telstra signal but you are not able to get a Optus signal. In our submission, on no view could that be said to be immaterial, insignificant, irrelevant.''

But Optus counsel Peter Jopling QC said the ad clearly relates to the percentage of Australians covered, rather than the entire Australian landmass, and people were unlikely to conclude that both networks covered almost all of Australia.

"Now, the two giants of the telco industry here have been slugging it out and talking about population reach for some time now to the public. The nature of that battle has focused on the use of percentages to talk about population reach and not in the context of geographical reach,'' Mr Jopling said.

"One thing you can be assured of is that the ordinary viewer knows when he has been out camping or he has been up at his farm that he doesn't get coverage in certain spots," he said.

"The case is all about people - Telstra to Optus, and people are looking at this thinking, 'Well, am I really going to switch? Are they telling me that I can now get coverage in the great outback of Australia?'

''But the bottom line of what they are trying to tell Your Honour is that Australians are going to be confused into thinking they can get coverage in close to 100 per cent of Australia ... as we all know from personal experience, that ... just couldn't be so.

''Dare I say it, there are some of us who can't get coverage in parts of suburban Melbourne, indeed the city of Melbourne."

Mr Jopling also rejected Dr Collins' assertion that the voiceover in the ad was deliberately fast, saying: "It's not an ad like the insurance, the banking or the election advertisements for the political parties on both sides of the divide where the disclaimer is down the back, is spoken in rapid-fire tone. Nothing is placed or said obscurely."

Justice Elliott reserved his judgment. Optus will continue to not run the ad on its website or book further ads.

- with David Ramli