What will happen if I put none for payment type on iPhone?

What will happen if I put none for payment type on iPhone?

You won't be able to purchase apps on your phone, unless you have a gift card. This is ideal for parents with children that do not want for their children to buy a lot of In-App-purchases (as those can add up), but you can always add a credit card or debit card to your account in settings>account>view>payment information.

Nothing, that just means you can only download free apps.

Nothing. Just means you are limited to using iTunes cards to make purchases within the Stores