I'm not sure how it works in the UK, so I apologize in advance if the system is a little different than what I can suggest.
I do know here that T-Mobile has their own stores, and some of them have service centers. You might see if they can take your phone and restore it to original factory standards.
We do update our phones in conjunction with the carriers, so firmware updates may be available. Third-party firmware updates? I wouldn't. Third party regular applications might be better.
I do know that most, if not every phone has a keycode option to restore the default factory settings. How to access that for your particular model isn't something I have, but your carrier does have it.
What you might do is call in, say that you're ready to give the phone to a friend (or received it), and you want to start fresh, and could they assist with defaulting the phone back to factory settings - but I suggest doing it from a landline, and not the phone itself.
Keep me posted.
I have been given a Samsung SGH-D600E phone (a hand-me-down:) which is a T-Mobile branded (UK) version.
I have deleted all the SMS tones from the phone with the original idea of putting my own on it. However after using the file manager software to put midi (.mid) files in the downloaded sounds folder on the phone, I do not have an option to select them.
(Although the phone can play them if I browse them in the file manager on the phone)
So how do I either a) restore the original files b) use my own mid files (preferred)?
I have read that you can utilise a firmware update to improve the phone, but these are implemented by 3rd parties and thus I guess not sanctioned by Samsung?
Or is it because the midi files need to be a certain type?