Back in 2016, I decided to finally give in and get myself a smartphone. One of the reasons for this decision was that I wanted to offer customers on fairs the possibility to pay via card - and to do this with relatively small financial and logistical overhead, you need a smartphone.
So I did some looking, and some research, and I tried to find a phone with replaceable battery (as this can be one of the first things to give out, and being able to replace the battery means you can use the phone so much longer), relatively small so it would fit well in pockets, with decent battery life and not too highly priced. I finally ended up with a Samsung S5 mini - and I was quite happy with it.
Until... well. Until at some point, it did not get proper reception anymore. Even in places where it should have gotten very good reception - nothing. Some head-scratching and some internet research later, I had found that the phone has two antennae built inside, one for the "slow" stuff and one for the "fast" stuff (3G), and the fast antenna had died a quiet death. This was annoying, but no big deal - I changed the settings to never use the fast connection, and there it was, functioning nicely again. Yes, the internet was slower now - but I never stream things anyways, and all the bits that I needed to download occasionally are quite small. (The Most Patient Husband found me a prepaid phone tariff that was very, very small and thus very, very affordable, and just the right fit for what I would need. It has 150 MB of free data each month, which is plenty for checking mails, writing a few messages, and even sending a few pictures when away from home; for everything larger, I use wifi connections. So I'm very much used to not sending or downloading huge things over mobile data - and whether getting the mail takes 3 or 6 seconds, well, that's no big deal.) It, however, meant more use out of the phone, and not needing a new one. Good for the environment.
My newfound serenity with the slow mobile data did not last very long, though, because apparently something else was giving up, and the phone became unreliable. It would refuse to connect, refuse to get messages or send them, and since that was one of the main uses for the phone when I'm doing stuff such as organising the Forum, I was getting antsy. I had expected the phone to last much longer than just a bit more than two years, which was making me quite unhappy - even though the thing itself still seemed like the perfect fit for my needs. My desire to spend another 180 or so Euros for a new phone of this make, for maybe another 2 years was, however, ... very small. So I got myself a refurbished replacement phone... the same model, used and with slight traces of said use, with a new battery, for about a third of the new price. Also I had hoped to just very easily transfer my old phone's contents to the new one. Same thing, should be easy, right?
The new phone arrived, and I found out that it was a branded one, with T-Mobile special software (sorry, apps...) on it. Well, no big deal. I managed to transfer my stuff (not as easy as I had hoped), and everything worked well for a bit. Then an Android update arrived, and afterwards, the phone would crash, or lag for ages until it reacted. Which is annoying for a phone that you want to use, but really and seriously not good for a phone used for, say, payment by card on a busy fair... One of the worst lags was about 14 minutes until I managed to access the home screen. So I was not happy anymore - but also did not want to buy yet another phone.
I finally decided that I could try to root the phone, in hopes to make things better - and reading the help pages and descriptions in an android forum, I found that there's a way to overwrite the phone OS with a newer or different version (an un-branded one, for instance), which would not lose any data, not change the OS, and not void the warranty (not that I have one, but good to know). It's called "flashing", there's a tool that Samsung offers called Odin (hah!), you download the proper firmware, follow the instructions and hope that it works.
That's what I did... and it looks like that was successful. So in case you have similar troubles because your phone had some hiccup when the last firmware update arrived... you might want to trust in Odin making everything better, too.