在非洲，移动电话通话费用都是预付的。

Nearly all airtime in Africa is pre-paid.

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我们知道通过竞争可以降低通话费用，提高服务质量。

This shows that competition can help reduce the cost of the phone calls and also can help improve the quality of services.

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越来越多的竞争也让通话费用有了大幅的下降。

More competition should drive prices for calls down dramatically.

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