"The first day Kindle was announced, our sales outstripped earlier records," he said.

As for whether a smaller smartphone is harder to read than a Kindle, Pendergrast said, "Don't tell that to our customers," since the vast majority read on a smartphone or PDA. Fictionwise has found that many of its buyers read for hours on smaller devices, buying "multiple books" each month.

Another factor with Fictionwise readers is that most read on multiple kinds of devices. Even if they own a Kindle, they still might take only a multiuse device such as a smartphone on a trip for reading an e-book. "Some [handheld] sizes are very small, but the BlackBerry Storm or Touch or the iPhone is more than sufficient," Pendergrast said.

Jack Gold, an analyst at J.Gold Associates, said he could understand reading a book on an iPhone for 15 minutes, but reading text for four hours "would make my eyes pop out."

Rob Enderle, an analyst at Enderle Group, said much the same thing, pointing out that LCD screen displays on smartphones are not as clear as those of a Kindle or Sony e-reader.