Sometime around 1979 or 1980 someone gave me a slip of paper with a phone number and said "Dial this with a modem."

I did, it answered "Pentagon TIP," and before too long I was roving around the ARPANET. If memory serves me right the main command was "C" for connect. You simply typed "C" and a small number, and then logged in as "guest"/"guest" (the world was smaller and more innocent back then). I'm fairly certain that I logged in to a system at UC Berkeley.