Here's another one I coincidentally just found. Remember the radio dispatch voice on the police series Adam-12? (She was heard at the beginning of every episode - "One Adam-12, One Adam-12, see to the woman...")

Turns out she wasn't an actress but a real police dispatcher. Her name was Shaaron Claridge, and she would frequently change her voiceovers to make them more accurate. 

"Claridge explained that she wanted her dialogue to sound as realistic as possible. Whenever a script contained something that didn’t match actual police communication, she adjusted the wording to reflect how dispatchers spoke on the job."

‘Adam-12’ Fans May Not Know The Familiar Voice Behind The Police Radio Was A Real LAPD Dispatcher