Google is slowly opening up the Play Store's billing policies. The "user choice billing" pilot program that was announced in March is now accepting sign-ups. Google describes the program in a support article, saying, "This pilot is designed to test offering an alternative billing option next to Google Play's billing system and to help us explore offering this choice to users. We are looking to gain feedback in different countries and ensure we can maintain a positive user experience."
Developers interested in billing through an alternative provider can fill out Google's sign-up form, and it sounds like Google will manually review each application. Currently the supported regions are the European Economic Area (that's Austria, Belgium, Bulgaria, Croatia, Republic of Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, and Sweden), Australia, India, Indonesia, and Japan.
Google won't let developers use the pilot program for games—the biggest money makers—but only for apps.