When did the PRR discontinue use of its system of inductive train phones? And how fast was the equipment (in particular, the visible "handrail" antennae along the roof) removed from rolling stock equipped with it? Glancing at PRR locomotive photos on George Ellwood's "Fallen Flags" rail image site (invaluable resource!) I saw a couple of locomotive photos dated 1965 and 1966 that showed the antennae, but the 1967 and later photos that I checked didn't have them. (But I only checked a few.)
The PRR indicated in its employee timetables which towers had radio. Among what I have I found the following:
Western Region TT No. 5, effective Oct. 30, 1966, and
Central Region TT No. 4, effective Oct. 29, 1967.
In the reference marks for the List of Stations at the beginning of the timetable, the Western Region TT from 1966 shows a capital O for trainphone, a solid 5-pointed star for radio, and a star in a circle for radio and trainphone; the Central Region TT from 1967 shows only the star for radio. CUSTER tower, on the Panhandle west of Mingo Junction, appears in both timetables, with radio and trainphone in 1966, but only radio in 1967. CRESTLINE also appears in both timetables, but with only radio in both years. Apparently there was some overlap as radio was phased in, but trainphone appears to have been discontinued by fall 1967.