Stop me if this sounds implausible even for a Damon Lindloff movie, but right after BlackBerry finally shipped BlackBerry Messenger (BBM) for iOS on Monday, Apple's iOS 7.0.3 update broke it on Tuesday. Adam Zeis on CrackBerry:
The heat of the issue lies with the font that BBM uses, "HelveticaNeue-Italic", and the fact that it was removed in the 7.0.3 update. This is causing various issues within BBM on iOS and making it crash in certain scenarios.
BlackBerry is aware of the issue and working on a fix. Hopefully they ask for and get an expedited review and the updated gets posted at Facebook speed.
Meanwhile, BBM for iPhone will be unstable and annoying. Where exactly HelveticaNeue-Italic went is another question...