Sprint should shed the superlatives for its wireless network in its ads, the National Advertising Division (NAD), an industry self-regulatory council, declared in a statement on Tuesday. The NAD recommended the wireless carrier drop the terms "brand new," "all-new" and "America's Newest," as well customer satisfaction claims, from its marketing.

The decision came after T-Mobile, Sprint's boisterous rival, challenged the advertising claims.

"We are pleased the NAD has acknowledged the many substantial technological improvements we have made to our network, which we continue to make. We will take the NAD's recommendations into consideration," said a Sprint spokeswoman.

Sprint is several years into an expensive network overhaul, which is partially responsible for its considerable customer loss. But the NAD says the network upgrade does not justify the descriptor "newest." It went on:

NAD recommended that the advertiser modify advertising featuring improved performance claims – "faster data speeds," "better call quality," and "fewer dropped calls" – to clearly disclose that the basis of comparison is to Sprint's own prior network.

Finally, NAD recommended that the advertiser discontinue the claim that it is "the most improved U.S. company in customer satisfaction, across all 43 industries, over the last six years."

John Legere, T-Mobile's CEO, frequently taunts Sprint. Last month, on an earnings call, he said his fourth-placed carrier would surpass the competitor in size "by the next month or two."