What if what they want to do with the device they paid for is modify it to send on licensed frequencies? Do any android devices use open source firmware for th

What if what they want to do with the device they paid for is modify it to send on licensed frequencies? Do any android devices use open source firmware for their cellular radios? I was under the impression that all cellular radios worked only with closed source firmware + closed source radio driver, in which case _you already_ can't modify some of the software on any android device?