Boy, that was an intense 10 minutes.
Another tech found an undocumented Raspberry Pi connected to a locations firewall. Ran around looking for answers, turns out the phone vendor sometimes uses them as a local monitoring appliance. Even so, apparently they're only tolerated as long as they're well behaved. This place was having network issues, so the network cable got oopsied.
@scottlink *shrug* I checked with our service manager. They're allowed to install them, and we're allowed to disconnect them when they cause problems.
Vendor is getting cut off very soon anyways.