If you're not a fan of giving Google your payment information, or your card/bank of choice isn't directly supported, Google Play has allowed carrier billing for a few years now. This means that when you buy an app/book/movie/etc, the payment would be charged to your phone bill.
Google has updated its list of direct carrier billing partners to include Telcel, one of the large major wireless carriers in Mexico. The page also mentions that Omantel, a major carrier in Oman, is now supported.
- Google Play Help