We used to have a number similar to the local hospital and a local car dealer, the same numbers, but two transposed.
Fortunately as we both worked full time and the children were out at school all day, they didn't bother us too much as the answerphone message made it very clear we were neither hospital nor garage. However if I had a midweek day at home, it could sometimes be really irritating, because, as others have said, people do not believe you when you say you are not the person/place they wish to contact.
For several years my parents used to get woken up every night with a phone call to a fax machine, somebody had obviously misdialled a number into the automatic send out memory of their fax machine and whatever was sent out at night was sent to them. Whoever should have received it, clearly never missed it. BT were completely unhelpful and it was before the 1471 system. In the end they would unplug their phone when they went to bed and replug it in in the morning