Setting mp3 to call in iOS?

Question

iOS

I recently found out that in iOS you cannot put an arbitrary mp3 file with a ringtone on a non-jailbreak-chickpea iPhone (you need to convert and cut it). Several questions arose:
1. Is this really so? can you put any mp3 file on the call?
2. Why is there still no program that allows you to put any mp3 file on a call? Is this due to limitations imposed by Apple or is it not possible to do this with the existing API? Maybe such a program exists, but I just don't know about it?

Answer 1

What's stopping you from converting to m4r?
If the phone is not jailbroken, then we convert it through audiko.ru, and put it in the tuna, and then we synchronize it.
If the body is broken, then convert it entirely through itunes to m4a, then change the extension to m4r, and put it into the phone through ifunbox.