Hardware far outlasts software in the smartphone world, due to aggressive chronic designed obsolescence by market abusing monopolies. So I will never buy a new smartphone - don’t want to feed those scumbags. I am however willing to buy used smartphones on the 2nd-hand market if they can be liberated. Of course it’s still only marginally BifL even if you don’t have demanding needs.
Has anyone gone down this path? My temptation is to find a phone that is simultaneously supported by 2 or 3 different FOSS OS projects. So if it falls out of maintence on one platform it’s not the end. The Postmarket OS (pmOS) page has a full list and a short list. The short list apparently covers devices that are actively maintained and up to date, which are also listed here. Then phones on that shortlist can be cross-referenced with the LineageOS list or the Sailfish list.
So many FOSS phone platforms seem to come and go I’ve not kept up on it. What others are worth considering? It looks like the Replicant device list hasn’t changed much.
GraphineOS seems to set the benchmark for secure de-googled android phones and has a very short list of supported devices. I think I’d suggest starting with one of those, and once support eventually drops, if you’re comfortable with a reduced security capability, looking to lineageOS or similar. I think if Graphine supports a phone, it’s pretty much guaranteed to have support on the more general OSs.
For a while I looked at ruggedized smartphones (some with removable batteries!) that were supported by lineageOS and others. I didn’t find one I was convinced would hold up as long as I wanted, and I had security concerns so I ended up getting a decent secondhand phone with guaranteed security support for a few years and putting it in a good case.
Sometimes I check in on various raspberry pi smartphone projects. I love the idea and think it’d probably be able to last the longest (or be turned into something else after an upgrade) but I don’t think any feel reliable enough to me yet.