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T-Mobile USA should stop claiming that it has “America’s Best Unlimited Network,” the advertising industry’s self-regulator said today.

AT&T challenged T-Mobile’s ads to the National Advertising Division (NAD), which ruled that T-Mobile hasn’t substantiated its claim that it has the best wireless network.

T-Mobile defended itself by arguing that speed outweighs all other factors—apparently including overall coverage and reliability. But to reasonably claim that one has the best overall network for unlimited data, a carrier should prove that it also has the widest geographic coverage and best reliability, the NAD concluded.