A somewhat newish iPhone would be more powerful than the raspberry pi. And I have got good use out of the pi for hosting game servers for small numbers of users. You can also get old apple devices way cheaper than new equivalent single board computers.
And the iPhone has a built-in touch screen, wifi, bluetooth, two cameras, internal storage, a GPU, a bunch of sensors, a giant battery, physical buttons, speakers, microphone, a giant market for third-party peripherals, cases, chargers, mounts, etc...AND it's way easier to get your hands on an iPhone (especially an old one) than a Raspberry Pi today.
Sure, getting everything to work in a Linux port wouldn't be easy, but it does clearly show the value of such a thing.
I wonder about the implications of running them in an "always-on" configuration. Would it be possible to remove the battery and run them entirely on AC power? If you could do that, you might be able to have some pretty nice low-power home servers.
If you just want a server, you can use an android phone already. Either pick one that works with postmarketOS, or termux could work fine (I don't know the overhead of that though). No point in using an iPhone here.
Assuming they're ok with being kept on 24/7, they could become IoT terminals. A 10 years old phone should still have enough horsepower if it contained the bare minimum to load just one program that speaks to the home network, or a mpd remote to play music in the given room, communicate through VoIP with other terminals, etc.
They could be used also in a lab to show data coming from instrumentation, as secondary display for servers etc. Plenty of uses; the only limitation being represented by the roadblocks (binary blobs, lack of documentation, closed drivers etc.) corporations put in place to prevent any further use of those devices that goes beyond what they have planned.
I removed the battery cell from a Samsung battery and powered the battery IC with the nominal DC cell voltage from a power supply.
The phone then indefinitely showed a full battery.
This might also work with an iphone
I've thought of using older Pixel phones for something like this. One annoying downside is that the Pixel devices do not tend to have an easy way to enable hdmi out.
And as a bonus they come with GPS, compasses, accelerometers, and of course network connectivity, out of the box (if you can figure out how to access them, anyway).
