Wireless Review has a nice overview:
The M:Metrics research re-affirms some widely held beliefs about specific applications, while providing hints on where they might be going: Ringtones continue to be among the most popular content applications; gaming interest continues to boom; news and information applications are broadly appealing; enterprise e-mail usage is spreading beyond executive suites; and short message service (SMS) usage is finally taking hold in the U.S.
But, the research results also pose many questions: Has the ringtone business peaked, and will the music industry force an extreme makeover? How can the wireless industry make more money from gaming? Is there an informational killer app? When will mobile messaging service (MMS) usage explode? What will it take to create enterprise e-mail ubiquity?