BlackBerry's rollout of BBM for iOS and Android has been shaky to say the least. The app was announced in May and delayed. Then released, pulled and delayed again. Today BlackBerry has announced that BBM is finally ready. However, to ensure there isn't a repeat of September's problematic release, there's a bit of a process.
The September release was plagued by security and server issues thanks to a leak of the Android .apk. To combat this, BlackBerry has instituted a queue for the BBM app. If you have already signed up for the app, you can get access to BBM right now. The rest of us will have to get a place in line, and wait until you receive an email confirmation from BlackBerry. It may be an annoying step, but given how long BlackBerry fans have been waiting, it's a minor inconvenience.
You can find BBM in the App Store right now.