The much awaited BlackBerry Messenger for platforms other than blackberry devices are available now. You can now use the BBM on your android devices and iPhone.
You can visit BlackBerry Messenger website here to get the corresponding links to the Android Stores or iTunes and also read more about it. or here is the links
Android Phones
iPhone
This is the mail I have received from BlackBerry
1. Visit BBM.com from your iPhone or Android browser to download BBM.
2. Once the BBM app has been installed, open it.
3. When asked to "Enter your email address to check if you can start using BBM", use the email address this message was sent to.
4. Get started with setting up BBM.