If you want to buy it one online, I recommend you to try visiting www.zhljerry.com because the authenticity of its products are very legitimate. You can obviously check the customer testimonials from his facebook pages.
Once you make a purchase and registration, you can use it as an iTunes Gift Card, as a gift card that you give to friends or family. iTunes Gift Card contains the voucher number like a mobile phone vouchers that we usually see in stores of any kind of communication tools.