Default [Q] Writing Custom Baseband

My apologies for repeating this question as I am not sure I posted it in the right location

I was wondering if you can help me in a project I am about to start

I am sure a lot of you are aware of Osomcom projects and OsomcomBB in specific, a great project with great potential.

The only annoying thing about it is its use of legacy phone hardware that is hard to find or has a relatively high cost.

So I was wondering what prohibits the development community from porting this to other phones. I think that on the physical layer it is still the same components. So what is stopping this from happening

I am interested in doing this but have no idea where to start, I don't know if this would be OS related or processor related or phone related. and I don't know how to write or modify the baseband and where the baseband resides (Firmware, ROM, OS), What programming language should/could this be written with.

Can any one point me to the right direction

Regards,
Hassan