Since I have no experience with GNU/Linux phones (only Android/Linux) but you're also interested in desktop answers: just look at what other paid software does

Since I have no experience with GNU/Linux phones (only Android/Linux) but you're also interested in desktop answers: just look at what other paid software does that runs on Linux. When I go to sublimetext.com I just click buy and it gives me the option of paying for it with credit card or paypal. Or Atlassian's on-prem option: you just go to the site, pay for it, then get what you paid for. Keep it simple, no need for anything novel. Another example is factorio: again just an up front cost (though they should have offered at least the option to pay towards upkeep costs because they do a superb job and the game is already really "done" and they keep releasing more and more minor features for free). If it's a subscription, the ongoing cost really needs to be worth it to me. I might donate much more easily than take a subscription, for example I pledged iirc 1% of K-9's (the email client) funding goal for a few months because I would like to get it out of its current stuck position even if I don't believe we need a person on an already-perfectly-functional email client working full time all the time. (I suppose here's at least one app example, though donations are of course not a business model. Then again, this is also about open source software, not a commercial app.) Paid support would be interesting pretty much exclusively to businesses, from my experience. In general I'd like to say that good support is worth money also for private people, but looking at how often I've paid out of pocket for software support of any kind... After buying a product I just expect it to work, and if it doesn't, then either they fix it or I get the money back and stop being a customer. Feature requests would be something to pay for, but then the rates of that compared to spending a few hours hacking it together myself are again not worth it. You'd need some sort of crowdfunding model where people pledge together towards features, and I fear that might be over-engineering it.