1) Administrators running their own instance that they can customize and have local conversations on, and
2) FidoNET, where instances relay messages to each other across a network.
I had worked on a similar network at the time which used Frontdoor in front of the BBS to call other boards and relay the messages (and receive calls from boards), but was never a part of the FidoNET network myself.
Haha - also "I was too scared of my parents" .. me too. There was not as much darkness as the skull images suggest, but trying to look 3l33t was /<-rad and all. RemoteAccess ("RA") was a nice software, I used that myself for a short time.
I remember that I had a strict limit of $13 a month that I was allowed to spend on long distance phone calls. I paid the bill myself, but my mother could not understand wasting more than $13 (I think it was originally $10, and I negotiated up to $13) a month on calling BBSs. I kept a hand-written log of how many minutes I spent in each area code and the price to call that area code so that I would not go over.