Direct carrier billing is one of the easiest ways users can buy apps, games, and other content on the Play Store. In countries where credit cards aren't readily accessible, where gift cards haven't been circulated, and where other methods of payments are either unavailable or not so attainable for everyone, having your operator handle the transaction for you makes things a lot simpler (although usually a bit more expensive thanks to added fees).

Two countries have recently seen direct carrier billing enabled for them: Vietnam and Kuwait. In Vietnam, the top mobile network Viettel has enabled carrier billing (they even have a friendly how-to on their site), and even though Google's support document doesn't mention it, it looks like the second largest operator MobiFone will do the same soon. In Kuwait, all three network operators are now supported: Zain, Ooredoo, and Viva.

If you're in one of these two countries and you don't have another means to buy some goods from the Play Store, now's the time to go check if your operator's payment method is active and start filling up on apps and games.

Source: Google Support

Thanks: Đức Thành