There was a significant BBM push that I recall last year[1]. I'd always heard great things about BBM, but it requires everyone to have a blackberry, no? That won't work in a diverse ecosystem; iPhone's Facetime is another example. These are standard features, not "killer" nor innovative features. Text messaging is the standard. Anything else can be had in an app (e.g. Kik Messenger [2]) that is at least cross platform.

[1] https://www.google.ca/search?q=blackberry+bbm+ads

[2] http://kik.com/