23% of all U.S. mobile subscribers say they’ve been exposed to advertising on their phones in the past 30 days, according to The Nielsen Company. Half (51% or 28 million) of all data users who recall seeing mobile advertising in the previous 30 days say they responded to a mobile ad in some way.

Here are some more bullet points from the survey:

• The number of data users who recalled seeing mobile advertising between the second and fourth quarters of 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)

• Asian-Americans and African-Americans are more likely to recall mobile advertising (42% and 40%, respectively) than all data users
• 26% of those who saw an ad responded at least once by sending an SMS text-message, the most popular ad response. 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
• 32% of data users said they are open to mobile advertising if it lowers their overall bill
• 13% (18% of males) said they are open to mobile advertising if it improves the media and content currently available
• 14% said they are already open to mobile advertising so long as it is relevant to their interests
• 23% expect to see more mobile advertising in the future (up from 15% in the first quarter of 2007)

The findings 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.