Network operator EE (Everything Everywhere) is being investigated by Trading Standards after a complaint was made about the firm's recent run of 4G adverts.
According to a report in The Telegraph, the complaint was made after posters declaring "4G is Here" were displayed in an EE shop in Plymouth.
Jon McKnight, the complainant, said the posters were "grossly misleading", as the nearest 4G signal is over 120 miles away in Bristol.
"I believe it is misleading in the extreme to suggest that an iPhone 5 bought in Plymouth would work on 4G and operate five times faster than on 3G when that service is not available here and no date has yet been announced for its introduction," he said.
EE is currently the only mobile operator offering 4G in the UK and the firm has previously vowed to make the service available to 16 cities by Christmas.
Plymouth Trading Standards are reported to have backed McKnight's claim, adding the ads were likely to cause problems nationwide.
"The use of the word here' could be misleading," said one of its officers.
A spokesperson for EE told The Telegraph that the wrong poster had been displayed in Plymouth. "We have over 700 EE stores across the country and would like to stress this was an isolated error for which we apologise. The poster has since been removed."
The spokesperson went on to add that the company is trying to build awareness of the EE brand, which means it will have to advertise in areas where 4G is not yet available.
"It is important that we raise awareness of the new brand and network through a national campaign across the UK, even in areas that do not have 4G coverage," the spokesperson said.
"However, we won't be advertising 4G overtly in those stores that are not in 4G covered areas."
