My work number at a former job was one digit off from a nearby pediatrician's office. I got calls intended for them at least once a week.
One year, my husband's dorm phone number was the same as the 800 number for the Polaroid building down the street. You wouldn't believe how many idiots couldn't comprehend that if you want to call an 800 number you first have to dial 1-800.
He bitched at Information Services and they changed his number.
About a year ago, I had a huge problem with Old Navy. Turns out some guy named Jorge (may he roast somewhere warm) opened up an Old Navy credit card, ran up a lot of charges, and skipped out on the bill. For whatever reason, they had my landline as his number. So they were calling ME asking for Jorge. And they wouldn't take "there's no one by that name here" for an answer. Finally I got it through their thick skulls that they had the wrong number. So they stopped calling me - but they put my number on their telephone advertising list.
And then there was the time I got about 25 voicemails on my cell phone from some chick. Apparently, some guy had picked her up at a bar, had his fun, decided he didn't want to see her again, and gave her a made-up phone number. Which happened to be my cell. Which has an outgoing message recorded in a female voice. And which happened to be switched off (I turned it off because I was flying, and forgot to switch it back on when I landed). She left TWENTY-FIVE voicemails over the span of about 48 hours. She was practically begging him to call her back. In several of the messages, I could hear little kids screaming in the background. No wonder he didn't want to see her again.