Carrier billing lets you buy apps, music, or subscriptions and have the cost...

https://ellasexcellentcolumns.quantlynix.com/posts/why-does-carrier-billing-feel-faster-than-card-checkout

Carrier billing lets you buy apps, music, or subscriptions and have the cost added directly to your phone bill. If you use a pay-as-you-go plan, the purchase amount is taken from your available credit instead