Many companies use Windows Live Messenger for corporate IM because it's free and comes with pretty much any Windows computer they purchase. Windows Mobile users have had mobile IM love for awhile, but BlackBerry users have been left out, at least as far as official messengers go. They had already been promised an official client, and today Microsoft published it. Also included is live Hotmail support, for those who still use it. Go and download it, BlackBerry addicts, if you haven't already. [Download, via Ars]