The market for pornography on mobile phones is expected to increase at a brisk clip worldwide through 2010, but a research firm says it will remain a small market as fans opt for bigger screens and other advantages of the wired Internet.

Spending on adult-entertainment for cellular phones is expected to increase to $5 billion by 2010 from $400 million in 2004, Strategy Analytics Inc. said. The market is expected to reach $1 billion in 2008.

Nevertheless, the research firm said it expects the demand for adult material to be largely met through wired Internet services, even though publishers, such as Playboy and Private Media Group, are expected to offer wireless services to paying customers.

"Adult services are not a killer application in waiting," Strategy Analytics analyst Nitesh Patel said in a statement. "With so much free pornography available on the fixed Internet, and mobility conferring only limited advantages to adult content, we believe that demand for adult material will continue to be largely met by fixed Internet services."