A new study claims that 23 percent of all U.S. mobile subscribers say they have been exposed to advertising on their phones in the past 30 days.

That translates to 58 million consumers who have recalled seeing ads on their mobile phones, according to Nielsen Mobile. Half of all data users who recall seeing mobile ads in the previous 30 days said they responded to a mobile ad in some way, the market researcher said.

"Mobile is yet another tool at marketers' disposal to drive either their brand strategy or their direct response strategy," said Jeff Herrman, Chicago-based vice president of mobile media at Nielsen Mobile.

The report found that the number of data users who recalled seeing mobile ads between the second and fourth quarters of 2007 grew 38 percent to 58 million subscribers, from 42 million.

Teen data users ages 13-17 were the most likely age segment to recall seeing mobile ads, Nielsen Mobile found. Forty-six percent of that age group recalled seeing some type of mobile ad versus 29 percent for all data users.

Asian Americans and African Americans, at 42 percent and 40 percent, respectively, are the ethnic groups most likely to recall mobile ads than all data users.

Nielsen Mobile found that 26 percent of those respondents who saw an ad responded at least once by sending an SMS text message, which is the most popular ad response.

Nine percent said they have used click-to-call to respond to a mobile ad, following a link on their phone to call a cited number.

Interestingly, 32 percent of data users said they are open to mobile advertising if it lowered their overall bill. Thirteen of the respondents -- 18 percent of males -- said they are open to mobile ads if they improved the media and content currently available.

This point is key, since most consumers have reached saturation point with subscription services -- for their mobile phone, cable connection, Internet access, magazines and so on, per Mr. Herrman.

"That's how this market will really grow -- driving information through the advertising model and not subscription," he said. "The advertising business model ... drives discovery."

Equally important, 14 percent of the respondents said they are already open to mobile ads as long as they are relevant to their interests.

"It's also important to make sure it's relative and relevant to other media," Mr. Herrman said.

Twenty-three percent expect to see more mobile advertising in the future, an increase from 15 percent in the first quarter of last year.

The findings were reported in the biannual Mobile Advertising Report from Nielsen Mobile. The survey polled more than 22,000 active mobile data users who used at least one non-voice mobile service in the fourth quarter.

Nielsen examined consumer recall, responses and attitudes toward banner ads on mobile Web pages, SMS text message ads, sponsored applications, video ads and other advertising that consumers see while using data applications on their phone.

"Moibile is the Swiss Army knife of entertainment and communications," Mr. Herrman said.