Well, thing is, BB is a "phase"... Black berry phones are unbelievably limited now, and people are more looking at iphones...
Nokia is still a big player in SA (nostalgia?), but people are using cross platform IM, having BBM is amazing, if your friends have BBM too, otherwise, people just move to Whatsapp because they realize that there's a bigger user base... no need for that horse-shyte bar code, and it's pretty stable..... It does have it's down times, I know all to well, but it's something that will reach a peak, then get better as Whatsapp servers increase in size and the growth of the app starts to decrease.