Remember those happy days when you could dial part of a telephone number and then listen to the noises down the line. The clunks and clicks as other people sharing the same cable dialed numbers with their rotary dials. You could also hear noises from within the telephone exchange if the equipment you were using wasn't properly adjusted or cleaned - adjacent selectors would rattle the wipers on your equipment as they stepped and you would hear strange clunking and clangs. But if you were really lucky you would get a 'crossed line'...
Here are a few samples I've managed to find from those bygone days!
AC9PIP1 - the little snippet of 2280Hz you could hear when an STD call answered.
Cable Fault Evington 1989 - One night all the phones were 'dead' and all we could hear were other people trying to make calls. In the end people started using it like a CB radio and here you can hear local lads chatting up the ladies...
Transit2 - These MF signalling noises were used to route calls around the country using 4 wire switching to minimise line signal loss. They weren't supposed to be heard by the customer but sometimes it bled through and here we have a good example.
Crackles - This one has it all!
VOIPBad - and here's something to show that although technology has moved on things can be just as bad now!