According to Gartner, mobile email will become more widely used than text messaging although "it may be quite some time until mobile email completely overtakes SMS."

This is an interesting story (via Information Governance) that is more about the continued adoption of wireless email than it is about it "killing" SMS.  The safer prediction here is that 20% of all email accounts (some 350 million) will be wireless by 2010.  I think the point made in the comments to this story is spot on.

Email will continue to be widely used but I’m not ready to sound the death knell for text messaging as a result of increased email usage via mobile devices.  While I am not a heavy text messaging user, I do use it and the next generation of workers depends on it.  How those personal communications via text message will displace or replace email is yet to be seen.  There will be an evolution to different ways to message, communicate, and share files based on the action required, the recipients targeted, and sensitivity of the content.