Three has been banned from describing its DC-HSDPA network as "3.9G" by the Advertising Standards Authority (ASA), after rival operator EE complained.
EE said the adverts, which were featured in the press, online and across the Tube network, implied Three's service was very close to 4G. It also protested that its "ultrafast network is built for more" tagline could not be substantiated.
In response, Three said 3.9G was not a technical term but used to describe its own DC-HSDPA network and claimed this was "one step below 4G technology".
The mobile firm defended its use of the term "Ultrafast" and argued it was "intended to communicate that the network speed and the type of technology used were only one side of the story and that other network factors could also influence levels of speed and quality for customers."
The ASA ruled the claim "3.9G" was misleading. It said while the ads didn't state 3.9G was an industry term, the claim did imply that Three's 3G DC-HSDPA network technology and speeds were very close to that of 4G, and superior to those offered by 3G technology in general.
"Three had provided information on the differences between DC-HSDPA and 4G LTE technology. However, the document was largely theoretical, and did not contain evidence of the actual measurable speeds offered by Three's network and how this compared to typical 3G and 4G speeds," the ASA said in a statement.
The organisation said it had not seen evidence to support such claims. It also ruled against Three's assertion its network was "built for more" and agreed with EE that this could not be substantiated.
"The ad qualified the claim with the statement 'our Ultrafast network is built to give you all-you-can-eat-data' but we had not seen any evidence that the offering of all-you-can-eat data plans by Three was the result of technological capabilities of their network beyond those of Everything Everywhere," the ASA ruled.
The ASA told Three the ads must never appear again in their current form and that it must ensure future claims do not mislead.
An EE spokesman said: "We're pleased the ASA agrees that this ad was misleading."
