http://zqktlw5bf6oycxq6qod452xnvdfcqhfwliz54bkul736g6b454jrk2ad.onion/wiki/index.php?title=Physical_Interaction
The problem with this system is twofold. First off, obtaining a wiretap warrant is pretty much a rubber-stamp process with little real oversight; and second the fact that the mass-surveillance infrastructure built to support CALEA is easily subverted to criminal and even rogue-state ends.