> it was impossible to obtain an address without providing some service or newsletter on a specific subject to the sysop in return

Huh? Not when I joined in my region. I didn't have to provide anything.

I was 14, but the BBS owner and mostly old guy heavy metal user base only found out when I later showed up at their annual user group meeting - and we had lots of fun (and drinks) together! They even took me clubbing later with a fake ID, and I woke up heavily wasted in the BBS owner's student apartment and we had microwaved frozen pizza together. Fun times.