This seems like a suspect denial. How do her lawyers know the call wasn't made from her office? Do they keep records of all calls made from the office, 24 hours a day, 7 days a week? If so, have they turned those records over to police? If not, how do they know?
It would take 2 minutes to examine the phone-records and ID the call (if it occurred from that office). I used to be the monthly phone audit guy for a Pentagon agency, and I’d get a listing each month of all calls going outside of the building. You knew the phone number from inside the office, and the time-stamp on the call. So unless, they’ve reviewed this document (I seriously doubt it), they can’t say for sure that the call occurred or not.
But for this robo-sounding voice mixer, this is an odd part on the story. Why use this?