Carrier billing lets you buy digital goods or services using your phone. The...

https://wiki-global.win/index.php/How_Do_I_Decide_When_to_Use_Carrier_Billing_vs_a_Card%3F

Carrier billing lets you buy digital goods or services using your phone. The cost is added directly to your monthly phone bill or taken from your pay-as-you-go credit. This means you don’t need a credit card or separate payment app