I worked many years in Verizon Security Unit. When I first started wiretaps for the FBI I would send data or content in X.25 format. They had to get a router and translate the X.25 and configure it using only the B Channels and ignoring the D channel of an ISDN circuit. I also would demand a faxed warrant even if I was doing the tap from my home. It came down when the warrant said so, and that pissed them off.
Late 70’s to early 90’s?