There is no SIM card at all, ever. Most US CDMA phones don't have a card, although there are some 4g "world" phones by Verizon that do have SIM cards. I'm not sure what info the SIM card contains, but I think that the same date (phone number, serial number etc.) are coded into the firmware through a "secret" menu what the phone is sold and activated. When the phone is resold, it has to be reactivated through the carrier who reprograms the data into the phone either in a store or OTA.
Now that I know what avast is looking for, I'll keep the boxes for the SIM behavior unchecked and relay upon the SMS commands if the phone is lost or stolen.