Go read on HelloPeter - All the complaints about BlackBerry BIS - rather use BlackBerry on Pre-paid that way you won't get any hidden suprises - just make sure you've zero airtime when you start downloading podcasts,you tube videos via an Application on BlackBerry APP world and I download mp3s downloaded around 500 meg of mp3 and tons of porno videos.
I won't be moving from BlackBerry ever - I am seriouslygetting value for money even after checking the new prices of data.
That's why you'll see a lot of people with BlackBerry who do the wise choice. I already got everyone in my office to get a BlackBerry - and that is around 30 sign-ups.
The trick is to not be on contract and if you do want a BlackBerry ask them nicely to not Bolt on BIS and MTN can do that for you - they automatically charge R69/59 on contracts.