This article suggests in-app purchases as a good way to get revenue on otherwise free apps.
In-App Billing Can Boost Android Revenues More Than You Think- Mobile Technology News «
“an “Android is free” mentality that comes with the Google brand.”
Is it that bad? I hope not.
“Will Google app revenue payouts rival Apple’s billions? Not likely, at least not in the short term. But the new in-app billing functionality offers Android developers a chance at earning more money, something many have been patiently waiting for.”