Putting aside that there would be absolutely no conspiracy related purpose to turn the power and phones off for a few moments at the time of the assassination (and the Hertz sign was clearly working at that moment), her testimony is clear in context. Her job was to answer the phone. She is explaining why she could leave her desk for the moment to look out the window (no one was calling). If there were any doubt about the phones working, she walks down the hall but can't get the attention of a co-worker because - wait for it - she is talking on the phone! Rightly or wrongly Hine attributes no calls to be answered to the fact that motorcade was in town. Presuming most are out watching. Obviously, no one would attribute a phone and power outage to the motorcade. Good grief.
Miss HINE. Yes, sir: I was alone until the lights all went out and the phones became dead because the motorcade was coming near us and no one was calling so I got up and thought I could see it from the east window in our office.