BBM is a very widely used online service a bit like Google Talk, Twitter etc.
Since Twitter is currently valued at around 20 billion and RIM/Blackberry at 7.7 billion dollars, salvaging the BBM service is probably smart.
That said, they should have done this years ago as it was pretty obvious:
- BBM was everywhere
- it was desirable (reasonably easy and lets you reach many people easily, no per message charge)
- iPhones and Androids were starting to be everywhere too and make BBM less desirable
So this is most likely a case of too little too late. But maybe they can make Microsoft pay them to have a Windows Phone version