Oh gosh. I remember my parents hiding my keyboard and mouse after my Dad received a £500 phone bill one month. This was in 1999. We were on pay per minute dial-up in the UK and I was obsessed with playing a game called Team Fortress Classic, a mod for Half-Life. Even with ping times of 200ms it was still really playable! We only had one phone line and the downside of this for my parents was that no-one could call the house phone - engaged tone. Remember, this is before widespread mobile phones. The downside for me was that any time someone picked up a phone in the house - like my sister to call her stupid boyfriend - all they heard was modem noise and it sometimes ended up in the modem hanging up the connection mid game... Infuriating!
Luckily I had a spare keyboard and mouse in my cupboard, which I promptly set up to the bemusement of my parents. They were very patient...