It's not the world's most advanced mobile OS, but a good way to escape the Apple and Google ecosystems.
It is possible to purchase the OS and install it to Sony Xperia phones. https://shop.jolla.com
Not enough people value openness to make the trade off versus iOS and Android.
Does iOS not provide the privacy you need?
I think Purism would be satisfied with much less initial adoption on the overall market than somebody like Mozilla/Canonical. In short, they'd probably consider it a success much sooner. Also, both FirefoxOS and Ubuntu Touch were essentially adopting the same philosophy as Android in terms of having a closed-hardware approach and a software stack that while open in principle, was largely restricted on-device to run just the apps available in the respective app-stores, made for the platform specifically, which weren't that many.
Purism is making it so that practically any Linux app can be installed out of the box and with a small amount of work, any GTK3/4 app can be made touch friendly as well. I think this could provide them the app ecosystem head start they'd need.
> Not enough people value openness to make the trade off versus iOS and Android.
I think you're, sadly, right. However if PurismOS becomes a solid choice in its own right and then you have the privacy advantage on top, it might sell.
> Does iOS not provide the privacy you need?
Kind of, that's what I use now, however I have to trust Apple on keeping its word, which may be difficult considering they're moving more and more into "services" == rent seeking. Also, I have serious problems with the war on general purpose computing Apple is involved in and the closed nature of their software, where they have the ultimate say in what I can run on a piece of hardware I paid thousand pounds for to own, not rent.
Google oozes from every part of Android. I very much doubt that installing LineageOS with closed-source blobs for most of the hardware makes Google/NSA/OEMs completely unaware of your activity. Moreover, Android is such a critical piece of software that probably every significant 3 letter agency in the world has some sort of a backdoor in/to it. Android suffers a security fiasco quite often and the update situation is quite awful. Lineage is also often not as stable as one'd like and the update process from one major version to another can be itself nerve-wrecking.
On the technical side, it is running ancient, out-of-tree kernels that lack a lot of the security work going upstream, which is especially concerning considering there's a new Spectre variant patch in practically every release.
Lastly, having the full GNU/Linux experience in my pocket is something I've always wanted.
Whether 'regular users' care about this is not particularly concerning to me, as I think the 'enthusiast crowd' is large enough to get the ecosystem started and once we feel comfortable recommending this to our 'regular' family members and friends, they need not to be aware of any of the additional benefits - it would be just the new smartphone that they have.
Nevertheless, I hope that Purism will be able to deliver a product which is as easy to use as a "normal" Android device with those privacy/sustainability features as a bonus. That way I might be able to give the people who ask me which phone they should buy next some good advice.