It makes a lot of sense for smartphone users to be able to add the cost of their app or music downloads to their monthly phone bill.

This method of payment is known as "carrier billing." While some app stores, notably Apple's App Store, shun it, others have embraced it.

Google has been smart in recognizing that people would find this method of payment convenient, and has moved aggressively to broker deals with wireless carriers across Europe, East Asia, and North America to make carrier billing possible on Android devices.

At last count, Android users in 21 countries can pay for Google Play goods on their phone bills: apps, music downloads, and in-app purchases.

Carrier billing is often unfairly painted as a payment method that's mainly popular in poor countries where people don't have access to credit cards. But Google's work with carriers has actually focused on wealthy economies, with thriving app stores, including in Japan, the U.S. and the U.K.

The table below, compiled by BI Intelligence, shows the wireless carriers that Google has signed on to support this payment method, known as "carrier billing," which is proving more and more popular with consumers.



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Here are some key points from the full report:

The report also: