cell phone novels, characters tend to be undeveloped and descriptions lacking, while paragraphs are often fragments and consist of dialogue.

"Traditionally, Japanese would depict a scene emotionally, like ‘The train came out of the long tunnel into the snow country,' " Mika Naito, a novelist, said, referring to the famous opening sentence of Yasunari Kawabata's "Snow Country."

"In mobile phone, you don't need that," said Ms. Naito, 36, who recently began writing mobile phone books at the urging of her publisher. "If you limit it to a certain place, readers won't be able to feel a sense of familiarity."

Written in the first person, many mobile phone novels read like diaries. Almost all the authors are young women delving into affairs of the heart, spiritual descendants, perhaps, of Shikibu Murasaki, the 11th-century royal lady-in-waiting who wrote "The Tale of Genji."

"Love Sky," a debut book by a young woman named Mika, was read by 20 million people on cell phones or on computers, according to Maho no i-rando, where it was first uploaded. A tear-jerker featuring adolescent sex, rape, pregnancy and a fatal disease - the genre's sine qua non - the novel nevertheless captured the young generation's attitude, its verbal tics and the mobile phone's omnipresence. Republished in book form, it became the No. 1 selling novel last year and was made into a movie.

Given the mobile phone novels' domination of the mainstream, critics no longer dismiss them, though some say they should be classified with comic books or popular music.

Rin said ordinary books left members of her generation cold.

"They don't read works by professional writers because their sentences are too difficult to understand, their expressions are intentionally wordy, and the stories are not familiar to them," she said. "On other hand, I understand how older Japanese don't want to recognize these as novels. The paragraphs and the sentences are too simple, the stories are too predictable. But I'd like cell phone novels to be recognized as a good thing."

As the cell phone'sbook popularity leads more people to write mobile phone books, though, an existential question has arisen: can a work be called a cell phone novel if it is not composed on a cell phone, but on a computer or, inconceivably, in longhand?

"When a work is written on a computer, the nuance of the number of lines is different, and the rhythm is different from writing on a mobile phone," said Keiko Kanematsu, an editor at Goma Books, a publisher of cell phone novels. "Some hard-core fans wouldn't consider that a mobile phone novel."

Still, others say the genre is not defined by the writing tool.

Ms. Naito, the novelist, says she writes on a computer and sends the text to her mobile phone, with which she rearranges her work. Unlike the first-time cell phone novelists in their teens or early 20s, she says she is more comfortable writing on a computer.

But at least one member of the cell phone generation has made the switch to computers. A year ago, one of Starts Publishing's young stars, Chaco, gave up her phone even though she could compose much faster with it by tapping with her fingers.

"Because of writing on the mobile phone, her nail had cut into the flesh and became bloodied," said Mr. Matsushima of Starts.

"Since she's switched to a computer," he added, "her words have gotten richer and her sentences have also grown longer."

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