I've never heard of one, although that doesn't necessarily mean anything, since I don't know the people who manage it. According to the first hit on Google, it's located in E19, with extensions in 24 and NW12 (i.e., the usual places for network gear). I have no idea where in E19 it is, or how well-secured those locations are -- but phone blocks are exposed in a whole bunch of locations that are probably easier to access. There's also the additional challenge that many lines, particularly "class A" lines with unlimited access, are ISDN lines using the AT&T proprietary BRI signalling to communicate with 7506 desk phones. But telephone equipment is ancient history; who would want to mess with that when there are *computers* around?!
One story I can tell, as it was relayed to me by a hacker who was there: the original 7506es had a firmware bug. When the handset was off-hook, the built-in clock stopped running (presumably because they were using the same timer interrupt for the call timer). LCS was an early adopter of the ISDN phones, and my colleague told me that AT&T sent a technician to every office in the building to extract a ROM from each phone and replace it with a fixed version. They tried to get one of the buggy ROMs to hack on; I don't recall if they were successful. (This would have been mid-1980s.)
But don't forget that hacking ethics would prevent them from doing anything so interesting as to have an impact on public safety.
Garrett A. Wollman | As the Constitution endures, persons in every snipped-for-privacy@csail.mit.edu | generation can invoke its principles in their own Opinions not those | search for greater freedom. of MIT or CSAIL. | - A. Kennedy, Lawrence v. Texas, 539 U.S. 558 (2003)