49 CFR §220.309

1. (a)The digital storage and display function of an electronic device to refer to a railroad rule, special instruction, timetable, or other directive, if such use is authorized under a railroad operating rule or instruction.
2. (b)An electronic device as necessary to respond to an emergency situation involving the operation of the railroad or encountered while performing a duty for the railroad.
3. (c)An electronic device to take a photograph of a safety hazard or a violation of a rail safety law, regulation, order, or standard, provided that—
   1. (1)A camera that is part of a cell phone or other similar multi-functional electronic device is not included in this exception unless it is a railroad-supplied device and is used for an authorized business purpose;
   2. (2)The camera, unless otherwise permitted, is turned off immediately after the documentation has been made; and
   3. (3)If the camera is used in the cab of a moving train, the use is only by a crewmember other than the locomotive engineer.
4. (d)A stand-alone calculator if used for an authorized business purpose.
5. (e)A medical device that is consistent with the railroad's standards for medical fitness for duty.
6. (f)A wireless communication device to conduct train or switching operations if the railroad operating employee is part of a crew assigned to a train that is exempt under § 220.9(b) from the requirement of a working radio when the employing railroad has fewer than 400,000 annual employee work hours.