很簡單...只要係itune choose 1 free app and download, it ask you to open a itune account, you can follow the step until in page of payment method, you can find there is an option that you can choose with "no credit card"
that's it.
you need credit card to register id but after register go back
phone setting ==> apple store to view account go to payment info choose none then will updated back to none payment in file