I remember that there were different networks you could get into using 800 numbers.  Once in, you could telnet to different networks and sites -- always in text mode.  Those 800 numbers were passed around like the phone numbers of "easy" girls.  Everyone wanted to share, but no one wanted the 800 line modems to be tied up. 

Other 800 numbers which were closely held were the ones which you could use to get into the AUTOVON system. 

Even better was knowing which AUTOVON operators at which DoD location would give you an "off net switch" and let you make a local phone system call.

When using an AUTOVON line to send data, you had to smooth talk the operator into not interupting the call and screwing up the whir-buzz-whir noises.  Sometimes this was hard if you didn't have the right priority.

Spoken like a vet who has 'Captain Crunched' the networks more than a few times, buddy!