Ever visited the Northern Cape, the biggest province in SA, almost half the size of the rest of SA? Towns are about 100 km apart. 10 km out of any town not on a national route, the signal is gone. Tracker doesn't work out of town either. Many areas of other provinces don't have cell signal either. There is signal along all major routes through these areas but go 10 km off the route and you are in signal silence.
If you look at the signal coverage maps, you will see what I'm saying. Al;so, don't assume the signal coverage in rural areas as indicated is good. It can go right down to 2G or be patchy. Dropped or non connecting calls are frequent.