Coverage - refers to the extent to which something including a location is covered - this case by mobile phone services. We also speak of insurance coverage which refers to the extent to which the occurrence of certain events or risks will lead to compensation. Broadcasters and journalists also speak of "coverage" of news; in this case the extent to which they cover and report on events. We can also refer to insurance "cover" for short. Some of these terms have become standard in certain industries so it is just a question of being able to recognise when they are used and not worry too much about the logic of their use/usage!

Coverage is commonly used in media context to explain how extensive research was on a specific topic. Example. CNN did a full coverage on the hurricane Katrina disaster. Meaning they researched the natural disaster in depth to report to their audience. I have never heard the term full coverage being used for make up.

to cover , in the context of your question . is to put/spread something over /on the thing you want to conceal /hide or protect . I want to cover my car with this because i dont want it to get wet when it rains . coverage is the noun of this word . But, the coverage of the car is only 90% since the cloth i used to cover the car is too small for the whole car . Good coverage in moblie terminalogy means it cover a good area that it is supposed to cover - that is the reception is good over a wide area . to use and usage is the same as above - one is a verd , the other a noun . eg I will use this phone because its coverage is good , even in remote areas ; but its usage is limited since the battery life is short . Full coverage cream ? A cream will always be able to cover your whole face if you apply it over your face , so i take it that the word "coverage" here has the other meaning which is protection as if you have been covered by it - hence protected . This cream has full coverage against any side -effects = has full protection . No ,full covered or full coverage cream are wrong because there is not such word as full cover and full coverage is a noun , and you cannot join it with another noun . But, you can say . I can use this cream and not afraid of anything because im fully covered against anything if this cream is not good or bad for me