According to the latest report from Neilsen Mobile, about 23% of U.S. mobile phone users have seen advertising on their cell phones in the last 30 days and about 51% of those users responded, in some way, to the ads.

Nielsen’s findings come from the bi-annual Mobile Advertising Report and are based on a survey of more than 22,000 active mobile data users who used at least one non-voice mobile service in the fourth quarter. In the report, Nielsen examined consumer recall, responses and attitudes toward banner ads on mobile Web pages, SMS text-message advertising, sponsored applications, video advertising and other types of advertising that reach consumers while using data applications on their mobile phones.

“Increasing levels of consumer recall, interaction and receptivity to mobile advertising reinforce the validity of the mobile marketing medium,” said Jeff Herrmann, vice president of Mobile Media at Nielsen Mobile, in a statement.

The study also found that: the number of data users who recalled seeing mobile advertising between Q2 and Q4 2007 increased 38% (from 42 to 58 million subscribers); teen data users (ages 13-17) were the most likely age segment to recall seeing mobile advertising (46% recalled seeing some type of mobile advertisement, compared to 29% of all data users); 26% of those who saw an ad responded at least once by sending an SMS message; 9% say they’ve used click-to-call to respond to a mobile ad, where users follow a link on their phone to call a specific number; and 32% of data users said they are open to mobile advertising if it lowers their overall bill.

“We see an increasing trend of consumers willing to trade off and receive advertising to gain more – and better – mobile content,” continued Herrmann. “Successful mobile marketers will meet the challenge offered by consumers by engaging with them in a way that adds value to the mobile user content experience.”