Disconnected Phone Numbers

Over the past few weeks I have received several strange calls on my cell phone.  The first was a phone call stating my car warranty was about about to expire.  I didnt find this too strange since I had just gotten a new cell phone and figured it had to do with the person who had the number before me.  I didnt pay much attention to the number that called, it happened a few more times but still didnt pay much attention.  Then about 2 weeks ago I got a call that I missed and tried to call the number back and a recording came on stating  "the number has been disconnected or is not in service at this time".  I thought it was strange since maybe 2 minutes had elapsed but I was busy at the time and just went on my merry way.  I have now received the same thing from 3 other phone numbers.  All of these numbers are registered to residences in different states if you do a reverse lookup online.  I found a website that is dedicated to these phone numbers as well as many other numbers all with the same issues.  People from all over have reported these same scenarios. Some people who have anwerered these have either had hang ups or people trying to sell them car warranties or free satellite systems.  It is all a scam but I was wondering if anyone else in the Montrose area has had similar experinces lately or if anyone knows how scammers are able to do this little trick.