I've been daily driving Linux phones for the last 18 years and I would never switch away. Sure, at the beginning it required you to make it your hobby, but you were being rewarded for it. Sometimes when I'm looking at Android/iOS devices being used over someone's shoulder I'm quite horrified at what I see and what people consider normal these days and so glad that my phone works for me rather than anyone else.
What do you use? both in terms of hardware and software. I love the idea of a linux phone but I'm very skeptical.
I'm currently using a Librem 5 with PureOS 11 and Phosh. PureOS is a bit behind on software releases compared to other available distros, but I find it to be the most polished and stable experience.
In the past I have used a Neo Freerunner (with Om2007.2 and later SHR) and then a Nokia N900 (with Maemo 5). The former demanded plenty of your attention but could be made to work well enough, while the latter was a really nice yet exceptionally hackable consumer device. Before I switched to a Librem 5 I had carried a second phone with Android for about 3 years as the N900 was already too old for comfortable web browsing and there was nothing else on the market that I'd consider worth switching to for a while - but that was the only such exception.
Was hoping someone mentioned the N900. The best keyboard i have ever used on a phone was the N900 physical slide-out. Maemo 5 also included word prediction and autocorrect features that just worked, perhaps its nostalgia but I always recall using that keyboard as a great tactile experience and great example of nokia build quality. Still have that phone with me.
What you can do with that phone that’s useful?
Everything I do online when I'm not in front of a PC I do on that phone. Web browsing, RSS, instant messaging, e-mail, social media, banking, navigation, public transport routing, TOTP auth, music playing, photo taking, weather checking, "smart" home stuff, conference agendas, occasionally some games or even software development (but not a lot these days - I used to program on my phone a lot when I was a teenager though). I even ran Jamulus on it to jam online during covid because it achieved better audio latency than my laptop, long before it got its Android port. Oh, and phone calling sometimes too, even though I've never been a big fan of that. Anything I need to, really.
And how is that any different compared to Android/iOS?
No tracking.
Everything happens on my terms. The phone never tries to grab my attention unless I explicitly make it so. All the things I use are FLOSS. I can patch anything I want down to the kernel and bootloader, often on the phone itself (see https://news.ycombinator.com/item?id=49191008). The OS is managed the exact same way the OS on my PC is and all my skills and knowledge directly transfer over, so I can script it or write applications the exact same way I did on PCs for decades. No "side-loading" shenanigans whatsoever. I can use any browser I want with any extensions I want. I've even used it at a game jam once - plugged a screen, keyboard and mouse in and made a game with the same tools I would have used on a PC (QtCreator, Allegro, GIMP, Inkscape, Audacity, LMMS) and cross-compiled it to Windows and macOS right from the phone using the exact same tools and workflow as usual.
I could probably go on and on. It feels like my little personal pocket computer rather than an appliance that someone lets me play with on their terms.
BTW. Funny how it can go from "it can't possibly replace Android/iOS" to "how is that different from Android/iOS?" :)