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" Me "Yes".
    Mike: "You've got the bytes swapped in the HMP password field."