Funny story of my youth: When the first payphones with digital terminal were introduced, I found that you could access the operator menu, that was password protected. For months I checked different combinations of those 5 secret numbers at different terminals after school, in a sequential order. One day I was in.

Inside the operator menu you could check how much money there was inside the machine, you could make free calls, but you could not take the money out. I never managed to take the money out without violence.

So I signed a mobile phone contract that gave you some call minutes the more calls you received (it was a hit back then, I think from Vodafone), and called myself repeatedly from phone to phone.