The concept of number spoofing has apparently not made its acquaintance with you.

FCC on Caller ID and Spoofing
 Jan 26th, 2012
Someone called me from this number asking about a certain car. Then asked me if I was at work.I just found out now that this could be someone cloning the number and only wanted to know if I was out of the house! Can someone really mask his real number using another existing number?
 Jan 26th, 2012