oh, i'd often wondered this too.
i've heard the tone at JFK as shown in the PHL video. But, there's at least another tone out there that I hear on a regular basis.
There's also one that's a constant tone. like, "ding, ding, ding" It's more synthesized compared to the one on the PHL vid, i.e. it sounds like an alert tone rather than an acknowledgment beep.