Payment Gateway With the Android? How does it work?

Having never developed on the Android or any mobile platform I was wondering how the payment gateway systems currently work?  Do I need to setup a authorize.net account that processes credit cards or do users just download an app and receive a charge on the statement?   I believe the iPhone ties there applications in with ITUNES cards so kids can actually use their itunes cards to also buy games. This is a huge plus imo for parents who dont want their kids downloading and ringing up a bill.  I'm still struggling to see how the developer ends up getting compensated whichever way the end user is paying? 

Just some thoughts for you developers out there creating games for kids...