How is someone else using my cell phone number to make marketing calls?

I keep getting calls from Califorinia from irate people who have received marketing calls from a home finance company offering services and my cell phone number is in their caller ID as the originating call. Cingular has no record of the calls being made and obviously I am not making them. I use my phone for business and do not wish to change the number, which is the only solution Cingular will give me. Any Ideas?

contact the attorney general in your state, the tellamarkerters have found a nother way of beating the systems {no call list} basically when they call you it comes up on the caller i,d, as somebody else so you answer the phone, but if you looked at the caller i,d, an it sayed tellamarketing you would not pick up the phone,,,,,,,, i know this cause when the phone rang the other day it sayed it was a lawyer out in vagas but it was a tellamarkter i called the number back an it was the secatary for the lawyer that was on my caller i,d. an she sayed they was getting hit hard with it to sooooo call the attorney general an file a complaint

{you need to change your number ,,,contact all your custumers an give them a new number an whenever you contact other people give them your new number}

thats impossible some must be doing it at home or something cuz u cant copy a sim card