Though at a previous job, I got on the elevator one day to hear a telemarketer's voice coming from the emergency speaker. I'm guessing it happens, but just very rarely?
I had something similar, twice. Once I was in the elevator when the emergency phone started ringing. I picked up, and it was the Seattle Times trying to sell subscriptions.
The other time, same elevator, it was someone asking for a specific person that I had never heard of.
In the case of the Target breech one had to be transferred to the unlisted extension first. So it's not as though it's a phone number exposed to the outside world.
The other time, same elevator, it was someone asking for a specific person that I had never heard of.