That leads me to the idea, that it would be nice if the Jolla store contained official support for sending donations. All my applications are open source and distributed for free - I just like them to be as widely available as possible.

And while they all have donation buttons in the respective About page in the application (PayPal, Flattr & Bitcoin ), not everyone has PayPal/Flattr or Bitcoin account, which might not be even available in their respective country and users are also not very likely to get it just to send a small tip to a favorite developer.

On the other hand, the store could either use carrier billing and/or a paired credit card, thus making donations quite a lot less painful for the users. Even if Jolla took a cut, it would still be IMHO a net benefit.

An example of this being already used somewhere could be the Mozilla Addons page, that has a built-in button for sending donations to Firefox Extension authors. It uses PayPal, but at least it is built-in.