two years ago i had a buddy working at mtn as a student engineer. i won't go into the details of this. at the time he asked me to keep this strictly confidential as it would have landed him in hot water. however he no longer works there, so here goes.
to cut a long story short, he was issued with an mtn sim card which enabled him free calls within the mtn network and calls to other networks were in the region of 20c-25c per minute. the interesting thing to note is that this is probably cost price - this should give an idea of what their profit margins are - and more importantly why they are so hesitant in revealing their mark-up to carte blanche.
granted his position at the time (still a student), one can safely assume that this is the same for all top management, as well as many other employees. this is the reason that management within these mobile operators couldn't give a **** about prices to consumers, because it barely touches their own pockets. as long as they get well paid, and receive basically almost free telephony, they quite frankly couldn't give a damn about anyone else.
however i noted that in the carte blanche insert, it said that next year they will all be required by law to open up their books to icasa. things could get really interesting really soon.