Well, it appears some people are waiting a very long time now for their activations to come through on their Android and iOS devices, so they can get started using BBM .
Well I just thought I would share what seems to be working for others, and has been reported elsewhere to work.
Force stop the app from the device, then restart the device, and re-open BBM. From there you should be able to re-enter your email address, and get started setting up your BBID and using BBM.
Its not my own idea, but seems to work, on Android at least. Not 100% about iOS.
To force stop an app on Android, do the following.
Go to settings
Select BBM from the App list
Press Force Stop on the apps page.