Is this a scam or annoying collection call?

[rz]

MacMagus nailed it. I'd bet it is legitimate, and is a collection agency. At the house I owned before my current one, I was getting these calls all the time, looking for someone named Gary. Apparently he used to have that number. I finally started asking if these were collection agencies and was told (reluctantly) yes. Then, about 6 months ago, I was getting them on my cell phone, looking for some woman. Since I rarely carry my cell phone, I was always getting messages. When I called the number, I had to tell them that I was not this person and had never heard of her, and that she probably gave someone my number either on purpose or mistakenly. The calls stopped immediately.

It looks like the calls may be legitimate based on the scenario you presented. I would address them as MacMagus suggested immediately.