The rise of reading on mobile phones is a hot topic at the Frankfurt Book Fair, and a new survey of readers by Publishing Technology shows that some 43% of respondents say they read e-books on their phones. But perhaps the most surprising finding of the survey is that Apple is giving Amazon a run for its money among younger mobile readers.

Overall, Amazon and Apple represent 81% of the mobile reading market, with the Kindle app enjoying a 50% to 31% total edge over iBooks. But among 18-24 year-olds, the split is nearly even, with 41% reading via the Kindle app, and 39 % reading on iBooks. And that gap could soon evaporate, given Apple’s device edge. The Apple iPhone was voted tops in the mobile device category of the survey, with 40% claiming to be iPhone users, with 28% owning a Samsung device.

And mobile reading is growing. The survey of 3,000 consumers across the U.S. and U.K. found that two-thirds are reading more on their phones than in the previous year (59% of U.K. readers, and 72% of U.S. readers).

At a session Tuesday at the Frankfurt Book Fair’s ConTec conference, Publishing Technology CEO Michael Cairns talked about the survey and its implications, noting that while mobile readers are currently a small slice of the overall e-book market, publishers should pay attention to the opportunity. With 2.4 billion mobile phones in use, they outnumber all Kindle reading devices by 120-1 margin. And with an estimated 35 million mobile phone users in the U.K., that 43% who said they read on their phones could translate to some 15 million e-books.

Perhaps most importantly, the survey also addressed why readers were not reading on their smartphones. “For publishers, it would be a bad supposition to anticipate that one who had a difficult experience reading on a phone would default to purchasing a print book,” Cairns observed. “It is about attention. On your phone there are many other areas the user can go to fulfill their attention, whether it be games, or videos, or social networking. So being able to present [e-book] content in the best possible way will guard against some of that other activity.”

The takeaway, Cairns stressed, is the extent to which the "very significant" opportunity for publishers with smartphone devices exists "beyond what we’ve seen with the Kindle." And, whether publishers are "concentrating enough on that opportunity."

The Mobile Book Reading Habits survey was conducted by OnePoll on behalf of Publishing Technology. The full results can be accessed here.

For those at the fair who want more on the survey, Publishing Technology’s Randy Petway will also chair a publishing panel discussion The Great Debate: How Much Money is in Mobile? on the Publishing Perspectives stage, Hall 8, at 2:30, tomorrow, October, 8.