I also have had similar experiences. The number of occurances lessened somewhat after I started including my name on my answering machine message, but I still get a fair share of non-paying-attention wrong number calls. Not only do I get calls for Jason, the guy who had my phone number at the fraternity before I did, I also get calls for Corey, who lived in the same room I did--but with a different phone number. Those always baffle me.

A large portion of these wrong-number calls are from telemarketers--they usually have you on hold until your message ends, thus missing your message and the point entirely.