Marketers increasingly understand the value of mobile ad campaigns, with local mobile searches on the rise among the ever-growing number of smartphone users. Nielsen reports 25 percent of the U.S. mobile audience used smartphones in Q2 2010, and marketers may soon be able to reach even more web-enabled mobile users. A new report from eMarketer suggests that mobile internet usage will be adopted by nearly half of U.S. consumers by 2014.

Initially, eMarketer had predicted that 83.5 million mobile users would visit the web from their devices in 2010, but the continuing popularity of the platform has led to a change in this forecast. Now, the research firm anticipates that as many as 85.5 million mobile users will visit the internet via smartphones this year.

Mobile internet use is expected to grow at an annual rate of more than 15 percent, suggesting it will become a regular practice for 40.3 percent of mobile users in 2011 and 53.9 percent by 2014. This translates into mobile internet access for 44.1 percent of the U.S. population within four years.

It also means marketers have the opportunity to reach a broad range of U.S. consumers with ads and mobile-optimized ecommerce content. Even more promising is that they may have the potential to generate sales among on-the-go consumers.

PriceGrabber.com’s recent Smartphone Shopping Behavior survey shows that mobile shoppers are increasingly buying on the go. In the first quarter of 2010, 13 percent of mobile users made online purchases via portable devices, compared to 10 percent last year. Moreover, an additional 22 percent of web-enabled mobile users anticipate buying items through their phones within the next 12 months.