Mobile gaming is quickly growing, with worldwide mobile gaming revenue for 2005 reaching $2.5 billion, according to eMarketer, which also cites a recent IDC forecast that U.S. mobile games revenue will increase to $1.5 billion in 2008, from $600 million in 2005. Among the main characteristics of mobile gamers, says eMarkter three are key: Women download more puzzle games - which drive the most mobile gaming revenue - than men; more than half of all mobile gamers are teenagers; and mobile gamers spend more on their phones than non-gamers.

"As location-based and multiplayer capabilities develop, advertising to wireless gamers will be an exercise in precision targeting, helping to drive the value of mobile gaming beyond the revenue associated with game sales or subscriptions," eMarketer writes.

"Powerful branding opportunities arise with the potential to reach a highly targeted audience wherever they happen to be, including, for the first time, places outside of home and work," says eMarketer senior analyst James Belcher.