The US is the global leader in mobile internet adoption, with 40 million US mobile subscribers (15.6 percent) actively using the mobile internet, according to a white paper (pdf) released by The Nielsen Company, reports MarketingCharts.

In 16 countries tracked, the US leads in penetration, followed by the UK (12.9 percent) and Italy (11.9 percent), according to the report, "Critical Mass: The Worldwide State of the Mobile Web."

Advertising is becoming a common part of the mobile internet experience: Some 26 percent of mobile internet users view ads while using the mobile internet, and mobile internet users are more receptive to mobile advertising than average data users, Nielsen Mobile said.

"With highly capable devices, improving network speeds and millions of mobile users visiting individual websites over their phones, we believe mobile internet reached a critical mass for mobile marketing this year," said Nic Covey, director of insights at Nielsen Mobile and author of the report.

"We believe the audience, inventory and planning tools are in place to make mobile internet marketing an important part of the media consideration set today."

It also identified the top 10 US mobile websites as of May 2008. Yahoo Mail, with 14 million unique monthly visitors, is the leading mobile internet channel, followed by Google Search and the Weather Channel:

Among other findings:

• The Motorola RAZR phones are the most popular phones among US mobile internet users, while Nokia handsets lead the market in Europe and Asia.
• Pricing plans with unlimited data packages are increasingly popular. Some 14 percent of US subscribers access the mobile internet with an unlimited data package, and 50 percent of data users say that they prefer the unlimited pricing model.
• 3G networks drive user satisfaction, and these networks improve data throughput speeds as much as six times, compared with 2 and 2.5G networks

About the research: Nielsen Mobile collects data on the mobile consumer and market through a range of methodologies, including surveying more than one million mobile subscribers worldwide, analyzing mobile bill behavior through an opt-in panel, analyzing network voice and data quality through drive tests, monitoring ad expenditures and messaging of the leading US carriers, and electronically metering the wireless activity of a mobile phone user panel.