I got over 4,000 users now on my open source noise android app psychoflute. But I gave it away for free, I'm working on an enhanced version with a cool opengl i

I got over 4,000 users now on my open source noise android app psychoflute. But I gave it away for free, I'm working on an enhanced version with a cool opengl interface I can sell, but I still plan on releasing the source, it doesn't violate GPL to sell the packaged version of your app while giving away the code, anyone can build from source and sideload on android, you're not selling the code you're selling the convenience of being able to load it via the android market without knowing about side loading.