How can I mod this to work with modern cellphone providers

I’ve searched online as well and didn’t find anything. I just don’t understand how people can make a phone from scratch but can’t make a phone from a phone haha. Was hoping someone on here had some solutions

The biggest problem in this kind of 'upgrade' is that the chips that receive and process the cellular signals in your old phone are not capable of handling the newer 4g or 5g signals. There's no upgrade path either; you won't find a 4 or 5g chip that will go into the space for the existing chip that's compatible with it.

And we haven't even gotten into the software issues; those chips require initialization and communication protocols that don't exist in your current phone and it's a virtual certainty that you'll never get the source code required to make the modifications that would be needed. Not to mention you'll have to become an expert at 4/5g protocols in order to properly write the new code.

TL;DR: No, it's not possible, at least not without tens of thousands of dollars in circuit board design and software engineering.

@cnp2438 Imagine you are given someone's notes, about 100 pages of notes. You are simply asked to translate the notes to another language. However, the person uses language weirdly, makes lots of abbreviations, and their handwriting is almost impossible to read. It might be easier for you to simply take the class and write your own notes, because you can understand what you wrote.