Your SIM, or Subscriber Identity Module, does have a number associated with it, called a SIM serial number (SSN). This number is also referred to as the integrated circuit card identifier (ICCID). ICCIDs are stored in the SIM cards and are also engraved or printed on the side of the card. The number can be up to 19 digits long and contains information about your operator, your location, and when it was made. The SIM is used to identify the subscriber with a different unique number, the International Mobile Subscriber Identity (IMSI).
Your International Mobile Station Equipment Identity (IMEI) number is different from your SSN, ICCID or IMSI. It is a unique serial number given to a device when it is manufactured that identifies a device on a mobile network, but not the subscriber. If your phone is stolen and you alert your carrier, they can blacklist the IMEI and prevent its use on all mobile networks even if a new SIM card is used.
The SSN or ICCID and IMEI information can be found under the Settings app on smartphones. On Android, go to the "About Phone" menu. On iOS devices, see “General: About” and on Windows phones, “About: More Info.” IMEI’s are often printed on a label under the phone’s battery as well.