Carrier billing lets you pay for apps, games, or services by charging the cost...

https://josuedumv023.tearosediner.net/how-did-carrier-billing-start-with-ringtones-and-games

Carrier billing lets you pay for apps, games, or services by charging the cost directly to your phone bill. Whether you have a monthly plan or use pay-as-you-go credit, the purchase amount shows up on your next bill or reduces your available balance