I know in some places they rely heavily on pay-by-phone services as a credit card alternative, even for face-to-face transactions. The cost of whatever they're buying gets subtracted from their phone credits and the phone company passes the money on to the actual business. I'm not sure how one would go about integrating this as a payment option for a phone app though, or if it's possible to do this without violating the Google Play agreements.

That would be awesome. I think if it were possible to buy apps through the pay-by-phone service, the local phone companies would have offered that service long ago.

In my country, you can use those to pay utilities and even some taxes. But you can't buy anything from outside the country (or really, from anywhere that doesn't have cellphone coverage for that particular company), and you can't pay in foreign currencies.

Yup!