I think this could be interesting. It's the possibility to buy things via your mobile phone bill.
In example, if you're on Android platform, clicking on a button "Buy" presents you with a confirmation window that says "Do you agree to pay $1.00 for whatever you're buying?", you say Yes and it's done. (it takes 1$ from you mobile phone account)
The thing with this is that it should work in most countries worldwide, with the issue of Google Play not allowing any payment methods other than their own hopefully being solved by a tolerance towards those countries where Google Play's payment systems don't work in the first place.
So I am trying to implement this in an Android app, with Kivy and Centili. Centili is one of the providers of this kind of payments. There are instructions for Android implementation and I am using Pyjnius to make this accessible from my Kivy app.
I made a small project on GitHub
https://github.com/squarrel/kivy-centili-android where I am in the process of trying to make this work. It will take some time tough, as I need to learn Java a bit more. You can find additional details there, follow my process, help speed it up and ask me additional questions here.
Cheers,
Milos