The api will be free for most people. If you use it for revenue generating transactions or it is core to your app (wouldn't be useful without it) we ask for a

The api will be free for most people. If you use it for revenue generating transactions or it is core to your app (wouldn't be useful without it) we ask for a revenue share (but no up front fee). Otherwise, as long as you don't hit our generous usage limits, it is free. The one exception is that contact sharing apps aren't allowed yet, although we have a plan to allow that in the next release.