BlackBerry Application Suite is software that runs on Windows Mobile devices that more or less turns them into BlackBerries, with email, RIM's instant messaging tool, and more. It also appears to integrate very well with existing Exchange accounts using Windows Mobile. It's even possible to run some BlackBerry applications.
My roommate sent me an IM: "Maybe BlackBerry for iPhone?" Which would be wicked smart, but unless Apple somehow lets RIM into the guts of the iPhone's OS, there's no way they could make an emulator that operates in a manner integrated enough to get anywhere close to what a real BlackBerry experience is like.
It's unclear when the BlackBerry Application Suite will be released, but if it's as polished as it appears it shouldn't be long. Then again, BAS was supposed to be out last year.