Inter-ISP/Telco/X.25 security procedures?

Oh it's worse than that :-).

At least as late as 1987, we knew each other's phone numbers (and in some
cases, network maps) by heart.

My favorite personal stories of this ilk are:

* c. 1986 I went into Dennis Rockwell's office (he worked down the hall
    from me on CSNET) trying to track down a TCP performance problem to
    another site. He pulled out a network map, pinged the intermediate
    routers (no traceroute in those days), sent a few specialized
    test packets, then called up the guy who managed the router (at
    another company) and told him his router was misbehaving and which
    bug was causing the misbehavior.

* c. 1984 I was writing a UNIX kernel implementation of HMP (the network
    monitoring protocol before SNMP). I'd just gotten the kernel to
    start sending packets, so I sent a poll (GET) message to a local
    router. I got no reply, so I sent the packet again.

    10 seconds later my phone rang. It was Mike Brescia at the BBN NOC.
    He said "Craig, are you trying to HMP poll 128.89.0.1?" Me "Yes".
    Mike: "You've got the bytes swapped in the HMP password field."

Craig