T'elevator app

So I was getting on an elevator the other day and got to hear the tail-end of an advertisement playing as it's emergency phone had been randomly dialed by an automated messaging service.
Yes, the elevator got spammed.
Oh it's true.

It got me to thinking that it should be possible to create an app which would have listed the numbers for all elevators in a give area and by typing in a current or known address you could phone that elevator whenever you wished.
You'd have your own custom piped in musak play-list for the rides.
You could prank your friends.
Speak with guests on the way up.

Oh the fun you could have.
wait...

Since the spam message I heard was audible without the receiver being lifted from the phone's cradle, I wonder if elevator phones are always on speaker mode and if this would let people hack and listen in on elevator conversations in public buildings?