49 CFR §220.311

1. (a)Notwithstanding any other restrictions in this subpart, a railroad operating employee who is in deadhead status and not inside the cab of a controlling locomotive may use an electronic device only if the employee is not using the device in such a way that interferes with any railroad operating employee's personal safety or performance of safety-related duties.
2. (b)A railroad operating employee who is in deadhead status and located inside the cab of a controlling locomotive must have each electronic device turned off with any earpiece removed from the ear—
   1. (1)When on a moving train;
   2. (2)When any member of the crew is—
      1. (i)On the ground, or
      2. (ii)Riding rolling equipment during a switching operation; or
   3. (3)When any railroad employee is assisting in preparation of the train for movement.