I had a look at these other threads and after making sure push notifications was off, and the master toggle under settings was turned to off, I haven't really had any more airtime sapped that I can tell. It seems to be staying still for the time being. I think those viber notifications were...
I have an MTN sim which I put in my iPhone 3G. I've noticed over time that slowly that airtime has been vanishing. I'm now down to less than R5. It ate up about R20. I don't use it much. It's just sitting still and losing airtime. It's my brother's and I'm just sort of trying it out before I buy...