Used calling minutes and mobile data are charged in the same way on your mobile subscription or prepaid card.
When you install a Mobile Coverage Extender in an area with bad mobile coverage, it can limit the intensity of the radiation produced by your mobile device to a minimum Why? Mobile devices consume less power if they receive a better signal from the network. With the MCE close by, mobile devices easily watch the mobile signal, so they emit less power. This way, the electromagnetic field they produce is much weaker than where mobile coverage is insufficient.