China will have more than 500 million mobile phone subscribers by next year—37% of the population. The country's dense urban markets are already saturated with mobile phones, and by 2010, almost half of China's 1.3 billion people will be using mobile phones, according to eMarketer's new report, China Mobile.

To demonstrate the ubiquity of mobile phone usage in China, when soccer fans in select countries in Asia were polled, almost a third of those in China said they planned to follow the World Cup on their phones. That's more than twice as many as fans in any other country polled.

In addition to the mammoth overall opportunity, marketers should note that 25% of mobile phone subscribers in China are between 20 and 24 years old. For marketers who want to reach these young adults, SMS is a good bet since 99% of respondents in a recent survey said handsets feature text messaging. But only 21% could play music on their phones. Ringback tones are a growth business, though. One mobile provider, China Mobile, hit $427 million for its ringback service by the second year of operation.

"Chinese notions of what constitutes cool differs considerably from the West, and not just in musical styles," says James Belcher, senior analyst and author of the report. He points to research that shows that music does not define cool as much as do clothing and overall culture.

In whichever manner mobile ad campaigns are executed, they should only be launched with a strong word-of-mouth campaign. "Word-of-mouth trumps even budget in terms of influencing purchase decisions," Mr. Belcher says.

Visit for more information on eMarketer's China Mobile.