You can still get updated software for CP/M, BeOS, DOS and OS/2 for crying out loud. Maybe not a lot, but people write / maintain that stuff. A relatively modern phone, running Linux? If it gains any adoption, I expect that the availability of apps won't be a problem. Maybe the ecosystem won't be quite as rich as Android or IOS, but it may well be "pretty good" which will be good enough for a lot of people.