I remember the dark ages when I owned a normal Motorola Razr flip phone. I was tricked into downloading some ringtones once and the charges were reflected on the monthly phone bill. I was so relieved that I could directly charge my credit card on the Android Market so my phone bill would not contain any nasty surprises. Turns out that some people actually like the option of direct billing though.
To that end, Google Play announced that more content than ever can now be charged via direct billing. You can now start downloading all kinds of content that won't show up until you receive your phone bill. Then you'll wish you could just pay immediately via credit card, especially if you have kids.
Consumers in the U.S. now have the ability to charge the purchase of apps, music, movies and books via T-Mobile. Japanese consumers can now pay for movies, apps and games via DoCoMo, KDDI and Softbank. Sprint will be joining this list very soon with their Android devices.
There are multiple mobile carriers in countries around the world who offer direct billing. If you wish to see your phone bill become inflated with app purchases, you can use the aforementioned T-Mobile and Sprint, as well as AT&T in the U.S. The UK offers similar services via T-Mobile and Vodafone. Check the Web site to see the full list of countries that offer direct billing services.
I'm still going to stick with paying for apps via my credit card. Just know that the option to use direct billing is there and will probably expand as Google expands its business. Maybe this will help Google Play in its attempt to make money. It's not doing so hot in comparison to Amazon or iTunes.