The BlackBerry Messenger (BBM) chat service is one of the factors that keeps many BlackBerry users loyal, but until now it has only been usable on BlackBerry devices -- a shrinking market however you look at it. Earlier this year BlackBerry announced plans to make BBM available for iOS and Android as well, and now we have release dates for that software.
A blog post from BlackBerry says BBM for Android will be released on 21 September, with the iOS version to follow on September 22. Those are US dates, so I'd add one for the Australian release, meaning Sunday and Monday respectively (the post suggests the iOS release will be timed for "each local market", but I'm a little suspicious of that). For Android, you need Ice Cream Sandwich or Jelly Bean; for iOS, you need iOS 6 or 7.
The initial release will include text chat, but not video; that's promised for a future version. Given the competition from platform-specific options (iMessage) and cross-platform texting alternatives, I'm not sure how widely this will be adopted, but it's a good way for BlackBerry to try and extend its reach.