"You may ask, why is BlackBerry doing this now?" asked Thorsten Heims, BlackBerry CEO. "It's a statement of confidence...It's time for BlackBerry Messaging to become a platform-independent messaging solution."
BBM on iOS will feature messaging and group management first, but BlackBerry plans to roll out additional features over the rest of the year, including voice, screen sharing, video, and the newest feature, BBM Channels.
BlackBerry claims that BBM now has over 60 million monthly active users, with more than 51 million people using BBM an average of 90 minutes per day, so it's a very active messaging ecosystem.
System requirements will call for iOS devices running iOS 6 or later, and it'll be a free download - assuming Apple approves the app, of course. But given then availability of other messaging products for iOS, it seems unlikely there would be a problem.