Carrier billing lets you buy apps, games, or digital content and charge the...

https://wiki-spirit.win/index.php/Can_I_Buy_Transport_Tickets_with_Pay_by_Phone%3F

Carrier billing lets you buy apps, games, or digital content and charge the cost directly to your phone bill. If you have a monthly plan, the purchase adds to your next bill. For pay-as-you-go users, the amount is taken from your prepaid credit