How old is "really old." As late as early 1950's in many smaller towns, all calls were by an operator and most phones were party line (more than one household per line). If you picked up the phone and heard your neighbor, the line was busy. Billing for home phones was on paper as it is today, except you saw the charges by call for any call that was a "toll" call (i.e., out of your immediate service area). You could also call collect. That was useful when using a pay phone; otherwise, you had to deposit coins for so many minutes and the operator would interrupt when your minutes were up. In small towns where all calls were operator assisted, phone numbers might not be 7 digits. In larger cities, I don't remember a time without 7-digit numbers. My home # in LA was Atlantic (AT)2-8441. Don't bother calling that number and asking for me.
In college, calls home (and to girl friends in other areas

) could add up, so the "twanger" was invented. It was usually made from a bent clothes hanger. I kept mine for many years -- maybe still have it. You inserted it through the coin return box and held a certain lever inside the phone that would return any coin that was deposited to the depositor. Operators became wise to that scam and would listen for the coins to drop. We then added cushioning to deaden the sound. Addition of the lever-protected box killed that activity.