Mobile device users are remarkably open to advertising on their phones. The biggest mobile marketing gluttons so far? It's iPhone users, according to new statistics from AdMob, a mobile Web site advertising provider.

Smartphone operating systems, overall, generated 34 percent of total US-based mobile ad requests in December, 2008. That's a 20 percent spike since last May. Of that 34 percent, 48 percent came from iPhone owners, according to AdMob's December metric report released late last week.

Research in Motion Blackberry users and Windows Mobile handset users follow with 19 percent and 15 percent US share respectively.

The research underscores a growing body of research that points to mobile as the next breakout area

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