We have an 800 number so our kids could always call us from wherever they were (got it before they each had cell phones).
Our number is one digit away from an American Express number that apparently is printed on the back of some cards.
We need to get our number changed. It seems to go in cycles. We go a long time with hardly any and then a streak of calls each day. Since American Express advertises 24/7 help line, we can get these calls any time day or night. Some of them are memorable. We have been sworn at in several different languages. Some people swear that they are NOT dialing wrong, even when we tell them that they are one digit off. Some are mad that we have an 800 number for a private residence.
We have a generic message on the answering machine, so they do not know immediately that they have the wrong number. This results in some interesting messages! Many, many people leave their account number and other personal info on our machine. People can get very angry that there is no live person to help them.
My all time favorite happened while DH and I were gone. DD #2 (age 17) came home from school to find about 13 messages from a very upset American Express customer. He went on and on about "24 hour" service and said that it must really be "23" hour service and he would call back in one hour. He did that all day. Every hour he would leave a message that said, "Well, I guess we are down to 21 hour service now, I will try again at 20 hours" He finally got super mad and demanded to have a supervisor call him back. He even decided that he wanted the CEO to call him personally. He swore a few times. Now, we have caller ID, plus he left his phone number about 12 times, so DD decided to call him back!!!

I can't believe she did it! She called him and told him she was the person he had been calling and leaving messages on her machine. He DENIED it! She told him he was dialing the wrong number and instead of being mad at American Express, he should have verified the number first. She also told him that she did not appreciate his use of profanity, which he tried to deny, but she offered to play them back for him. He then hung up on her!