Radio firmwares having full RAM access is an urban legend, at least on phones from the last 10 years. The baseband interface is actually done through a USB like

Radio firmwares having full RAM access is an urban legend, at least on phones from the last 10 years. The baseband interface is actually done through a USB like protocol. The legend ticks all the boxes of privacy minded/distrusting people and so remains popular, but it's not substantiated by any facts, at least not facts that pertain to modern smartphones from the past 10 years.