Under the federal hand-held mobile telephone restriction, what is a CMV driver prohibited from doing while driving?

49 CFR 392.82 (hand-held mobile telephone restriction) and 49 CFR 383.51 (disqualification sanctions); AAMVA CDL Manual Sec. 2.9.4, p.2-22

Many drivers assume any phone use while driving is equally illegal, but the rule specifically targets hand-held use. A CDL is not disqualified for a first conviction, that carries only a civil penalty of up to $2,750; disqualification kicks in after two or more convictions within 3 years, 60 days for the second offense and 120 days for three or more offenses, with a motor carrier that allows the violation facing civil penalties up to $11,000. Knowing the precise definition, and exactly when the license consequences start, has real financial and licensing consequences.