Dunno, I’m just not a Phone Guy, but I got a collection of old phones, some still sealed in the box, because a) I only do prepaid, and b) I typically get 2 at a time. I know I’m getting genuine mfr batteries, have a spare in case one phone crokes, and I have a spare battery if/when the original goes. Quite often, the same battery be used for different models within the same mfr’s lineup.
And you can get decent touchscreen phones like a Nokia Nuron or LG Prime, both of which have excellent mp3 players and are expandable at least to 32gig more. Both were <100bux each and included at least 50bux of airtime, and both are unlocked (need to keep it active at least 6mos to a year).
I just can’t see myself switching phones every year or two, relearning a UI, trying to move info from old to new (SIMs are great, but all the juicy stuff is in phonemem only, like b’days, etc.).
So those 2 are my “EDC phones” (trading off periodically), and each one has good/bad points. And both have excellent mp3 players. Both also have bluetooth, so I’m “untethered”.
So, you can probably pick up an older/used phone in good condition, and have a great mp3 player. No need to be as big as a pie-plate, either, as most newer bigscreen phones are.