Hello Ronaldo, If Apple was an all encompassing hardware, software, connectivity, internet, cable, telephone company, you would be able to buy airtime via iTunes. There has to be a line somewhere. This reminds me of the movie: Field of Dreams. In that movie the main character was advised "If you build it, they will come." Same with Apple. They built the iPad and they--you and and me, developers, publishers, movie studios, music labels, internet service providers like AT&T, Verizon (or whatever cellular data provider is in your country) came and bought.
There is a way to gift air time...here in the United States, you can buy airtime cards from AT&T, Verizon, Sprint, etc. You might want to check in with your provider and see if they offer gift cards.