Carrier billing lets you buy things using your phone without a credit card or...

https://nova-wiki.win/index.php/Is_Carrier_Billing_the_Same_as_Paying_by_Text%3F_Clearing_Up_Common_Confusion

Carrier billing lets you buy things using your phone without a credit card or app store account. Instead, purchases are added to your monthly phone bill or taken from your pay-as-you-go balance