Data usage in Tanzania and South Africa

In Tanzania, some were complaining about the high cost of mobile internet in Dar. I thought it was rather affordable, Airtel selling 1 week, 3GB packages for about 6 euros. In South Africa, which offered 3G already years ago, I expected the prices to have dropped significantly over the last few years. Not so. 2.5GB goes for about 40 euros. Yes, mobile data in South Africa is about 7 times as expensive as in Tanzania. 
Below are two charts detailing this.

Cost of mobile data in Tanzania

In Tanzania, Vodacom and Tigo offer packages for certain periods, limited through a fair use policy. Strangely, specifically Tigo is very tightlipped as to what 'fair use' means to them.

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