The world might be festooned with ads, but magazine covers had remained largely ad-free until this week, when a tiny Verizon Wireless ad appeared on the cover of Time magazine. The same ad is scheduled to land on the cover of Sports Illustrated on Wednesday.

Consumer magazines have for years flirted with putting ads on their covers, though when it's happened, the ads have usually shown up as cover wraps, in which an ad literally wraps around the cover, or a sticker that can be removed. But publishers have almost always avoided actually putting ads on their covers, because the real estate is thought of as the editor's first and best statement to readers, one that should be presented without interference from an ad. The influential American Society of Magazine Editors also advises its members to avoid the practice.

But the line seems to have been breached. And even though Verizon's ad is tiny enough that many readers might miss it, Time and Sports Illustrated's parent company, Time Inc., is shopping around ads that appear across the bottom of its other magazines, like Fortune and Money, according to people who have seen mockups of the ad.

Advertisers can safely be considered supportive of the idea, but the rest of the media business is still grappling with the idea. Here are reactions from five media figures:

"I think the cover is the latest frontier for exploration," said Joanna Coles, editor-in-chief of Hearst's Cosmopolitan, whose May issue included a peel-away cover for subscribers that was part of an ad buy for L'Oreal. "We'll see more magazines exploring how to use their cover," Ms. Coles added. "We wouldn't put a brand on the actual cover, but we would do a wrap. Each case should be taken individually to determine what works best for the reader."

"The truth is I don't think it's a big deal," said Victor Navasky, the George Delacorte Professor of Magazine Journalism at Columbia University's Graduate School of Journalism, where he directs the Delacorte Center of Magazines and chairs the Columbia Journalism Review. He's also the former editor and publisher of The Nation. "I think every publication has the right to decide how it uses its cover. I'm not worried about it being a slippery slope."

"To me, it is much more offensive to see ads pop up in the middle of stories that I'm reading on the web that to see part of a cover devoted to an ad," he added.

Andrew Essex, vice chairman at creative agency Droga5, questions why Tom Cruise appearing on the cover of a magazine is not ad for his latest movie. "Let's not oversell the purity of the church," said Mr. Essex, himself a former executive at The New Yorker, Details and Entertainment Weekly, in an email. "As long as there is no overt shilling, and the quality of the edit isn't ever compromised, the industry should by all means experiment and push the envelope. I think covers, many of which have become formulaic, should be shaken up as as a matter of evolution."

Jim Impoco, editor-in-chief of Newsweek, said a magazine's cover is the closest thing to art in the media world, but "someone's got to pay the rent." Marketers have asked about running ads on the spine of Newsweek, according to Mr. Impoco. And it's a tactic Sports Illustrated adopted earlier this year when it put a Lexus ad on the spine of its Swimsuit Issue. "I don't have any objection to that," Mr. Impoco said in an email. "As for the cover, it's not solely my decision. If we could avoid it, that would be great."

"Making a successful magazine cover is enough of a challenge," said Adam Rapoport, editor-in-chief of Conde Nast's Bon Appetit. "The idea of figuring out how to best incorporate an ad only complicates the process." Mr. Rapoport said he can imagine certain magazines, particularly weeklies, allowing ads on their covers without repercussions, just as newspapers like The New York Times and Financial Times have done. "But monthly magazines are different," he said. "They're supposed to be iconic and beautiful. Newspapers are important but ultimately disposable."