The FCC approved baseband chips run closed source software and do not have documentation for writing your own. So you need to reverse engineer the chip, write

The FCC approved baseband chips run closed source software and do not have documentation for writing your own. So you need to reverse engineer the chip, write your own software for it, and reflash it. But after reflashing it will no longer be FCC approved because some of the FCC requirements were implemented in software. So it will need to go through the FCC approval process again which can be very expensive. The alternative would be to create your own chip from scratch but that is even more expensive.