No use trying - I've tried for a year to get a better signal in Sandton CBD from MTN and I still can't hear my customers talking to me - constantly breaking up and my signal goes from Edge to 3G to Edge. Calls drop like it's going out of fashion.
I remember reading somewhere that they can't put up more towers in Sandton, 'cause there's no space or something rediculous, so it's probably a congestion problem, 'cause I have full signal, but bad reception if that makes sense. maybe that's what's happening in CT too.
I switched to Cell C, and walla, no issues - crystal clear voice and super fast data that never goes to Edge ever!