My fondest memory of 900 and 976 numbers was when I was about 10 years old.  I was huge into video games, and when I heard a commercial on TV for "action arcade", I knew I had to put a few quarters into that machine.  I ended up calling it about 8 times in a couple days before I realized that there were only 3 different outcomes no matter how many times I called.  I didn't think anything of it, but about a week or two later my mom asked me if I had been calling any phone numbers that I shouldn't have.  The phone bill ended up being $20 more than usual, and I was up shit's creek with a turd for a paddle.  A few years later, Robert Englund turned the 976 number on it's ear with his directorial debut  "976-EVIL"